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Probability Question

Help would be appreciated

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For p(a) i had 1/4 and p(b) i had 1/6 p(aub) i had 5/12 and for p(anb) i had 1/24

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Reply 2

aznkid66

Spoiler

EDIT: Wait, are you stuck on a certain part of the problem, or do you just want us to check your answers?
EDIT2: A and B are not independent events. Have you tried to find P(A n B) by multiplying the probability of the coin flip with the probability the dice role fulfills both criteria?

(edited 11 years ago)

Reply 3

megafobia

Original post by aznkid66

Spoiler

EDIT: Wait, are you stuck on a certain part of the problem, or do you just want us to check your answers?
EDIT2: A and B are not independent events. Have you tried to find P(A n B) manually?

Are my values right?

This was posted from The Student Room's Android App on my GT-I9300

Reply 4

aznkid66

Original post by megafobia

Are my values right?

This was posted from The Student Room's Android App on my GT-I9300

No. The probability of P(A n B) is the probability A occurs and B occurs. So the probability that the coin flip is heads, the dice rolls a prime number, and the dice rolls a 2. Because A and B are both affected by the dice roll, they are not independent events and thus it is not correct to multiply P(A) and P(B) to get P(A n B). Not to mention that part (ii) asks you to prove/disprove something, you should know that using the same method for both sides won't lead you to the correct answer..

Reply 5

megafobia

Oh yh they intersect since they share element {2}

Reply 6

aznkid66

Original post by megafobia

Oh yh they intersect since they share element {2}

Mhm. So really, P(A n B) is the probability the coin flip is heads and the probability the dice roll is 2. Then as you probably know you compare that value of P(A n B) with P(A)P(B).

Reply 7

megafobia

P(AnB) is just 1/4? And p(A)p(B) is 1/24 and hence this is false?

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Reply 8

aznkid66

Original post by megafobia

P(AnB) is just 1/4? And p(A)p(B) is 1/24 and hence this is false?

This was posted from The Student Room's Android App on my GT-I9300

It is false, but P(A n B) isn't 1/4. :P

Reply 9

megafobia

I need to find the p(2 on the die) which is 1/6

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Reply 10

aznkid66

Original post by megafobia

I need to find the p(2 on the die) which is 1/6

This was posted from The Student Room's Android App on my GT-I9300

Nope, that's P(B). (A n B) only includes the subset of B where A is also true, aka that there is a prime on the die (redundant within B) and that the coin flip is heads.

Reply 11

megafobia

Im really confused is it 1/12?

This was posted from The Student Room's Android App on my GT-I9300

Reply 12

aznkid66

Original post by megafobia

Im really confused is it 1/12?

This was posted from The Student Room's Android App on my GT-I9300

Yup.

Event A:
The coin is heads.
The dice is 2, 3, or 5.

Event B:
The coin is heads or tails.
The dice is 2.

Thus...
Event A and B:
The coin is heads.
The dice is 2.