# Mind Blown By Maths Example

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Okay so if you are given the probability of A and also P(B), then why does the example work it out from the equation P(A|B)??

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Okay so if you are given the probability of A and also P(B), then why does the example work it out from the equation P(A|B)??

**2630101**)Okay so if you are given the probability of A and also P(B), then why does the example work it out from the equation P(A|B)??

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**2630101**)
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I understand how to do all the rearranging the formula, but why cant i just do 0.5x0.9??

**2630101**)I understand how to do all the rearranging the formula, but why cant i just do 0.5x0.9??

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**2630101**)

I understand how to do all the rearranging the formula, but why cant i just do 0.5x0.9??

It depends on the situation if you should use this. If the probability of B changes given A has changed, you can't just multiple them together to find both probabilities (as the values are no longer the same!)

Spoiler:

For instance, if you were to toss a coil and roll a die,

P(Heads) = 0.5

P(6 on die) = 1/6

You could work out the probability of getting heads then a 6. You would multiply them together.

P(Heads AND 6 on die) = 0.5 x 1/6 = 1/12.

But it wouldn't make any sense trying to find the probability of getting a 6 given you have already got a heads. This is because the probabilities aren't affected by one another (they're independent).

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For instance, if you were to toss a coil and roll a die,

P(Heads) = 0.5

P(6 on die) = 1/6

You could work out the probability of getting heads then a 6. You would multiply them together.

P(Heads AND 6 on die) = 0.5 x 1/6 = 1/12.

But it wouldn't make any sense trying to find the probability of getting a 6 given you have already got a heads. This is because the probabilities aren't affected by one another (they're independent).

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**2630101**)

Okay so if you are given the probability of A and also P(B), then why does the example work it out from the equation P(A|B)??

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#12

You can't just multiply because

Multiplying out would work if these two events were

And also is this a

we are told that P(A|B)= 0.72

We are told that P(B)=0.5

simply substitute values in the formula: P(A|B)=P(A And B)/ P(B)

we get: 0.72= P(A And B)/0.5 ====> 0.36

Then that answers Part A of the question

Part B is virtually the same. You just change numbers.

**the probabilities depend on each other**. Ie. They are related. This is why simply**multiplying won't work**.Multiplying out would work if these two events were

**independent**. You really should know this.And also is this a

__or__**GCSE question**__? I ask out of pure curiosity!__**As Question**we are told that P(A|B)= 0.72

We are told that P(B)=0.5

simply substitute values in the formula: P(A|B)=P(A And B)/ P(B)

we get: 0.72= P(A And B)/0.5 ====> 0.36

Then that answers Part A of the question

Part B is virtually the same. You just change numbers.

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(Original post by

You can't just multiply because

Multiplying out would work if these two events were

And also is this a

we are told that P(A|B)= 0.72

We are told that P(B)=0.5

simply substitute values in the formula: P(A|B)=P(A And B)/ P(B)

we get: 0.72= P(A And B)/0.5 ====> 0.36

Then that answers Part A of the question

Part B is virtually the same. You just change numbers.

**TheNumbere**)You can't just multiply because

**the probabilities depend on each other**. Ie. They are related. This is why simply**multiplying won't work**.Multiplying out would work if these two events were

**independent**. You really should know this.And also is this a

__or__**GCSE question**__? I ask out of pure curiosity!__**As Question**we are told that P(A|B)= 0.72

We are told that P(B)=0.5

simply substitute values in the formula: P(A|B)=P(A And B)/ P(B)

we get: 0.72= P(A And B)/0.5 ====> 0.36

Then that answers Part A of the question

Part B is virtually the same. You just change numbers.

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