Tricky coin probability
Clash Royale CLAN TAG#URR8PPP
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Can someone please help, I am getting the wrong answer.
Consider four coins labelled as 1, 2, 3 and 4. Suppose that the probability of obtaining a ‘head’ in a single toss of the ð‘–-ð‘¡h coin is $ð‘–/4,, ð‘– = 1, 2, 3, 4.$ A coin is chosen uniformly at random and flipped.
Given that the flip resulted in a ‘head’, the conditional probability that the coin was labelled either 1 or 2 equals.
I tried doing this
P(coin 1 or 2 | tails) =
P(coin 1 or 2 And Tails)/P(tails)
=(1/4)(3/4)+(1/4)(2/4) / 1/4(3/4)+(1/4)(2/4)+(1/4)(1/4)
=5/6
In improved notation:
$$P(C_1 cup C_2 | T) = P((C_1 cup C_2)T)/P(T) \
= frac(1/4)(3/4) + (1/4)(2/4)
(1/4)(3/4) + (1/4)(2/4) + (1/4)(1/4) = 5/6.$$
But this is the wrong answer as the answer is one of 1/10,2/10,3/10,4/10.
How to do this?
probability statistics statistical-inference
add a comment |Â
up vote
3
down vote
favorite
Can someone please help, I am getting the wrong answer.
Consider four coins labelled as 1, 2, 3 and 4. Suppose that the probability of obtaining a ‘head’ in a single toss of the ð‘–-ð‘¡h coin is $ð‘–/4,, ð‘– = 1, 2, 3, 4.$ A coin is chosen uniformly at random and flipped.
Given that the flip resulted in a ‘head’, the conditional probability that the coin was labelled either 1 or 2 equals.
I tried doing this
P(coin 1 or 2 | tails) =
P(coin 1 or 2 And Tails)/P(tails)
=(1/4)(3/4)+(1/4)(2/4) / 1/4(3/4)+(1/4)(2/4)+(1/4)(1/4)
=5/6
In improved notation:
$$P(C_1 cup C_2 | T) = P((C_1 cup C_2)T)/P(T) \
= frac(1/4)(3/4) + (1/4)(2/4)
(1/4)(3/4) + (1/4)(2/4) + (1/4)(1/4) = 5/6.$$
But this is the wrong answer as the answer is one of 1/10,2/10,3/10,4/10.
How to do this?
probability statistics statistical-inference
Welcome to MSE. For some basic information about writing mathematics at this site see, e.g., basic help on mathjax notation, mathjax tutorial and quick reference, main meta site math tutorial and equation editing how-to.
– José Carlos Santos
Sep 1 at 17:46
I have tried to improve your notation. Please check that I have not changed what you mean to say. Change as necessary.
– BruceET
Sep 1 at 18:05
4
Hmmm I'm confused, it's given the flip resulted in a head so shouldn't you be solving for $P(C_1 cup C_2 |H)$ ?
– HJ_beginner
Sep 1 at 18:08
1
You solved it correctly, only as @HJ_beginner mentions, you calculated the wrong object.
– Stan Tendijck
Sep 1 at 18:19
Yes I actually read the question wrong and understood 'chosen and flipped' as the coin is tossed and then turned the other side to record heads
– Rahul Deora
Sep 2 at 7:54
add a comment |Â
up vote
3
down vote
favorite
up vote
3
down vote
favorite
Can someone please help, I am getting the wrong answer.
Consider four coins labelled as 1, 2, 3 and 4. Suppose that the probability of obtaining a ‘head’ in a single toss of the ð‘–-ð‘¡h coin is $ð‘–/4,, ð‘– = 1, 2, 3, 4.$ A coin is chosen uniformly at random and flipped.
Given that the flip resulted in a ‘head’, the conditional probability that the coin was labelled either 1 or 2 equals.
I tried doing this
P(coin 1 or 2 | tails) =
P(coin 1 or 2 And Tails)/P(tails)
=(1/4)(3/4)+(1/4)(2/4) / 1/4(3/4)+(1/4)(2/4)+(1/4)(1/4)
=5/6
In improved notation:
$$P(C_1 cup C_2 | T) = P((C_1 cup C_2)T)/P(T) \
= frac(1/4)(3/4) + (1/4)(2/4)
(1/4)(3/4) + (1/4)(2/4) + (1/4)(1/4) = 5/6.$$
But this is the wrong answer as the answer is one of 1/10,2/10,3/10,4/10.
How to do this?
probability statistics statistical-inference
Can someone please help, I am getting the wrong answer.
Consider four coins labelled as 1, 2, 3 and 4. Suppose that the probability of obtaining a ‘head’ in a single toss of the ð‘–-ð‘¡h coin is $ð‘–/4,, ð‘– = 1, 2, 3, 4.$ A coin is chosen uniformly at random and flipped.
Given that the flip resulted in a ‘head’, the conditional probability that the coin was labelled either 1 or 2 equals.
I tried doing this
P(coin 1 or 2 | tails) =
P(coin 1 or 2 And Tails)/P(tails)
=(1/4)(3/4)+(1/4)(2/4) / 1/4(3/4)+(1/4)(2/4)+(1/4)(1/4)
=5/6
In improved notation:
$$P(C_1 cup C_2 | T) = P((C_1 cup C_2)T)/P(T) \
= frac(1/4)(3/4) + (1/4)(2/4)
(1/4)(3/4) + (1/4)(2/4) + (1/4)(1/4) = 5/6.$$
But this is the wrong answer as the answer is one of 1/10,2/10,3/10,4/10.
How to do this?
probability statistics statistical-inference
edited Sep 1 at 18:09
BruceET
33.7k71440
33.7k71440
asked Sep 1 at 17:43
Rahul Deora
252
252
Welcome to MSE. For some basic information about writing mathematics at this site see, e.g., basic help on mathjax notation, mathjax tutorial and quick reference, main meta site math tutorial and equation editing how-to.
– José Carlos Santos
Sep 1 at 17:46
I have tried to improve your notation. Please check that I have not changed what you mean to say. Change as necessary.
– BruceET
Sep 1 at 18:05
4
Hmmm I'm confused, it's given the flip resulted in a head so shouldn't you be solving for $P(C_1 cup C_2 |H)$ ?
– HJ_beginner
Sep 1 at 18:08
1
You solved it correctly, only as @HJ_beginner mentions, you calculated the wrong object.
– Stan Tendijck
Sep 1 at 18:19
Yes I actually read the question wrong and understood 'chosen and flipped' as the coin is tossed and then turned the other side to record heads
– Rahul Deora
Sep 2 at 7:54
add a comment |Â
Welcome to MSE. For some basic information about writing mathematics at this site see, e.g., basic help on mathjax notation, mathjax tutorial and quick reference, main meta site math tutorial and equation editing how-to.
– José Carlos Santos
Sep 1 at 17:46
I have tried to improve your notation. Please check that I have not changed what you mean to say. Change as necessary.
– BruceET
Sep 1 at 18:05
4
Hmmm I'm confused, it's given the flip resulted in a head so shouldn't you be solving for $P(C_1 cup C_2 |H)$ ?
– HJ_beginner
Sep 1 at 18:08
1
You solved it correctly, only as @HJ_beginner mentions, you calculated the wrong object.
– Stan Tendijck
Sep 1 at 18:19
Yes I actually read the question wrong and understood 'chosen and flipped' as the coin is tossed and then turned the other side to record heads
– Rahul Deora
Sep 2 at 7:54
Welcome to MSE. For some basic information about writing mathematics at this site see, e.g., basic help on mathjax notation, mathjax tutorial and quick reference, main meta site math tutorial and equation editing how-to.
– José Carlos Santos
Sep 1 at 17:46
Welcome to MSE. For some basic information about writing mathematics at this site see, e.g., basic help on mathjax notation, mathjax tutorial and quick reference, main meta site math tutorial and equation editing how-to.
– José Carlos Santos
Sep 1 at 17:46
I have tried to improve your notation. Please check that I have not changed what you mean to say. Change as necessary.
– BruceET
Sep 1 at 18:05
I have tried to improve your notation. Please check that I have not changed what you mean to say. Change as necessary.
– BruceET
Sep 1 at 18:05
4
4
Hmmm I'm confused, it's given the flip resulted in a head so shouldn't you be solving for $P(C_1 cup C_2 |H)$ ?
– HJ_beginner
Sep 1 at 18:08
Hmmm I'm confused, it's given the flip resulted in a head so shouldn't you be solving for $P(C_1 cup C_2 |H)$ ?
– HJ_beginner
Sep 1 at 18:08
1
1
You solved it correctly, only as @HJ_beginner mentions, you calculated the wrong object.
– Stan Tendijck
Sep 1 at 18:19
You solved it correctly, only as @HJ_beginner mentions, you calculated the wrong object.
– Stan Tendijck
Sep 1 at 18:19
Yes I actually read the question wrong and understood 'chosen and flipped' as the coin is tossed and then turned the other side to record heads
– Rahul Deora
Sep 2 at 7:54
Yes I actually read the question wrong and understood 'chosen and flipped' as the coin is tossed and then turned the other side to record heads
– Rahul Deora
Sep 2 at 7:54
add a comment |Â
2 Answers
2
active
oldest
votes
up vote
2
down vote
accepted
Hint: The probability that a head is flipped is
$sum_i=1^4 P(text"coin i is chosen") cdot P(text"flip resulted in a ‘head’, ")$
$=frac14cdot frac14+frac14cdot frac24+frac14cdot frac34+frac14cdot frac44=frac58$
And the numerator is $(1/4)(colorred1/4) + (1/4)(2/4)$ since coin 1 and coin 2 are involved. You have used the probability of the third coin.
Therefore the answer of the question is $frac(1/4)(1/4) + (1/4)(2/4)frac58=frac3/165/8=frac310$
Thanks! I actually read the question wrong and understood 'chosen and flipped' as the coin is tossed and then turned the other side to record heads
– Rahul Deora
Sep 2 at 4:39
add a comment |Â
up vote
3
down vote
First we find:$$P(H)=sum_i=1^4P(Hmid C_i)P(C_i)=frac14frac14+frac24frac14+frac34frac14+frac44frac14=frac1016=frac58tag1$$
Then:
$$P(C_1cup C_2mid H)P(H)=P((C_1cup C_2)cap H)=$$$$P(C_1cap H)+P(C_2cap H)=P(Hmid C_1)P(C_1)+P(Hmid C_2)P(C_2)=frac14frac14+frac12frac14tag2$$
Combining $(1)$ and $(2)$ we find: $$P(C_1cup C_2mid H)=frac85left(frac14frac14+frac12frac14right)=frac310$$
Solving the right problem (+1)
– BruceET
Sep 1 at 18:23
Thanks! I actually read the question wrong and understood 'chosen and flipped' as the coin is tossed and then turned the other side to record heads.
– Rahul Deora
Sep 2 at 4:39
add a comment |Â
2 Answers
2
active
oldest
votes
2 Answers
2
active
oldest
votes
active
oldest
votes
active
oldest
votes
up vote
2
down vote
accepted
Hint: The probability that a head is flipped is
$sum_i=1^4 P(text"coin i is chosen") cdot P(text"flip resulted in a ‘head’, ")$
$=frac14cdot frac14+frac14cdot frac24+frac14cdot frac34+frac14cdot frac44=frac58$
And the numerator is $(1/4)(colorred1/4) + (1/4)(2/4)$ since coin 1 and coin 2 are involved. You have used the probability of the third coin.
Therefore the answer of the question is $frac(1/4)(1/4) + (1/4)(2/4)frac58=frac3/165/8=frac310$
Thanks! I actually read the question wrong and understood 'chosen and flipped' as the coin is tossed and then turned the other side to record heads
– Rahul Deora
Sep 2 at 4:39
add a comment |Â
up vote
2
down vote
accepted
Hint: The probability that a head is flipped is
$sum_i=1^4 P(text"coin i is chosen") cdot P(text"flip resulted in a ‘head’, ")$
$=frac14cdot frac14+frac14cdot frac24+frac14cdot frac34+frac14cdot frac44=frac58$
And the numerator is $(1/4)(colorred1/4) + (1/4)(2/4)$ since coin 1 and coin 2 are involved. You have used the probability of the third coin.
Therefore the answer of the question is $frac(1/4)(1/4) + (1/4)(2/4)frac58=frac3/165/8=frac310$
Thanks! I actually read the question wrong and understood 'chosen and flipped' as the coin is tossed and then turned the other side to record heads
– Rahul Deora
Sep 2 at 4:39
add a comment |Â
up vote
2
down vote
accepted
up vote
2
down vote
accepted
Hint: The probability that a head is flipped is
$sum_i=1^4 P(text"coin i is chosen") cdot P(text"flip resulted in a ‘head’, ")$
$=frac14cdot frac14+frac14cdot frac24+frac14cdot frac34+frac14cdot frac44=frac58$
And the numerator is $(1/4)(colorred1/4) + (1/4)(2/4)$ since coin 1 and coin 2 are involved. You have used the probability of the third coin.
Therefore the answer of the question is $frac(1/4)(1/4) + (1/4)(2/4)frac58=frac3/165/8=frac310$
Hint: The probability that a head is flipped is
$sum_i=1^4 P(text"coin i is chosen") cdot P(text"flip resulted in a ‘head’, ")$
$=frac14cdot frac14+frac14cdot frac24+frac14cdot frac34+frac14cdot frac44=frac58$
And the numerator is $(1/4)(colorred1/4) + (1/4)(2/4)$ since coin 1 and coin 2 are involved. You have used the probability of the third coin.
Therefore the answer of the question is $frac(1/4)(1/4) + (1/4)(2/4)frac58=frac3/165/8=frac310$
answered Sep 1 at 18:19


callculus
16.7k31427
16.7k31427
Thanks! I actually read the question wrong and understood 'chosen and flipped' as the coin is tossed and then turned the other side to record heads
– Rahul Deora
Sep 2 at 4:39
add a comment |Â
Thanks! I actually read the question wrong and understood 'chosen and flipped' as the coin is tossed and then turned the other side to record heads
– Rahul Deora
Sep 2 at 4:39
Thanks! I actually read the question wrong and understood 'chosen and flipped' as the coin is tossed and then turned the other side to record heads
– Rahul Deora
Sep 2 at 4:39
Thanks! I actually read the question wrong and understood 'chosen and flipped' as the coin is tossed and then turned the other side to record heads
– Rahul Deora
Sep 2 at 4:39
add a comment |Â
up vote
3
down vote
First we find:$$P(H)=sum_i=1^4P(Hmid C_i)P(C_i)=frac14frac14+frac24frac14+frac34frac14+frac44frac14=frac1016=frac58tag1$$
Then:
$$P(C_1cup C_2mid H)P(H)=P((C_1cup C_2)cap H)=$$$$P(C_1cap H)+P(C_2cap H)=P(Hmid C_1)P(C_1)+P(Hmid C_2)P(C_2)=frac14frac14+frac12frac14tag2$$
Combining $(1)$ and $(2)$ we find: $$P(C_1cup C_2mid H)=frac85left(frac14frac14+frac12frac14right)=frac310$$
Solving the right problem (+1)
– BruceET
Sep 1 at 18:23
Thanks! I actually read the question wrong and understood 'chosen and flipped' as the coin is tossed and then turned the other side to record heads.
– Rahul Deora
Sep 2 at 4:39
add a comment |Â
up vote
3
down vote
First we find:$$P(H)=sum_i=1^4P(Hmid C_i)P(C_i)=frac14frac14+frac24frac14+frac34frac14+frac44frac14=frac1016=frac58tag1$$
Then:
$$P(C_1cup C_2mid H)P(H)=P((C_1cup C_2)cap H)=$$$$P(C_1cap H)+P(C_2cap H)=P(Hmid C_1)P(C_1)+P(Hmid C_2)P(C_2)=frac14frac14+frac12frac14tag2$$
Combining $(1)$ and $(2)$ we find: $$P(C_1cup C_2mid H)=frac85left(frac14frac14+frac12frac14right)=frac310$$
Solving the right problem (+1)
– BruceET
Sep 1 at 18:23
Thanks! I actually read the question wrong and understood 'chosen and flipped' as the coin is tossed and then turned the other side to record heads.
– Rahul Deora
Sep 2 at 4:39
add a comment |Â
up vote
3
down vote
up vote
3
down vote
First we find:$$P(H)=sum_i=1^4P(Hmid C_i)P(C_i)=frac14frac14+frac24frac14+frac34frac14+frac44frac14=frac1016=frac58tag1$$
Then:
$$P(C_1cup C_2mid H)P(H)=P((C_1cup C_2)cap H)=$$$$P(C_1cap H)+P(C_2cap H)=P(Hmid C_1)P(C_1)+P(Hmid C_2)P(C_2)=frac14frac14+frac12frac14tag2$$
Combining $(1)$ and $(2)$ we find: $$P(C_1cup C_2mid H)=frac85left(frac14frac14+frac12frac14right)=frac310$$
First we find:$$P(H)=sum_i=1^4P(Hmid C_i)P(C_i)=frac14frac14+frac24frac14+frac34frac14+frac44frac14=frac1016=frac58tag1$$
Then:
$$P(C_1cup C_2mid H)P(H)=P((C_1cup C_2)cap H)=$$$$P(C_1cap H)+P(C_2cap H)=P(Hmid C_1)P(C_1)+P(Hmid C_2)P(C_2)=frac14frac14+frac12frac14tag2$$
Combining $(1)$ and $(2)$ we find: $$P(C_1cup C_2mid H)=frac85left(frac14frac14+frac12frac14right)=frac310$$
answered Sep 1 at 18:15


drhab
88.7k541120
88.7k541120
Solving the right problem (+1)
– BruceET
Sep 1 at 18:23
Thanks! I actually read the question wrong and understood 'chosen and flipped' as the coin is tossed and then turned the other side to record heads.
– Rahul Deora
Sep 2 at 4:39
add a comment |Â
Solving the right problem (+1)
– BruceET
Sep 1 at 18:23
Thanks! I actually read the question wrong and understood 'chosen and flipped' as the coin is tossed and then turned the other side to record heads.
– Rahul Deora
Sep 2 at 4:39
Solving the right problem (+1)
– BruceET
Sep 1 at 18:23
Solving the right problem (+1)
– BruceET
Sep 1 at 18:23
Thanks! I actually read the question wrong and understood 'chosen and flipped' as the coin is tossed and then turned the other side to record heads.
– Rahul Deora
Sep 2 at 4:39
Thanks! I actually read the question wrong and understood 'chosen and flipped' as the coin is tossed and then turned the other side to record heads.
– Rahul Deora
Sep 2 at 4:39
add a comment |Â
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Welcome to MSE. For some basic information about writing mathematics at this site see, e.g., basic help on mathjax notation, mathjax tutorial and quick reference, main meta site math tutorial and equation editing how-to.
– José Carlos Santos
Sep 1 at 17:46
I have tried to improve your notation. Please check that I have not changed what you mean to say. Change as necessary.
– BruceET
Sep 1 at 18:05
4
Hmmm I'm confused, it's given the flip resulted in a head so shouldn't you be solving for $P(C_1 cup C_2 |H)$ ?
– HJ_beginner
Sep 1 at 18:08
1
You solved it correctly, only as @HJ_beginner mentions, you calculated the wrong object.
– Stan Tendijck
Sep 1 at 18:19
Yes I actually read the question wrong and understood 'chosen and flipped' as the coin is tossed and then turned the other side to record heads
– Rahul Deora
Sep 2 at 7:54