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July 09, 2020, 12:11:27 pm

Author Topic: help with prob question  (Read 181 times)  Share 

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a weaponized ikea chair

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help with prob question
« on: May 29, 2020, 11:45:18 am »
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thanks   :)
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Sine

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Re: help with prob question
« Reply #1 on: May 29, 2020, 11:47:06 am »
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thanks   :)
What aspect of the question is difficult for you?

What working out have you done so far?

a weaponized ikea chair

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Re: help with prob question
« Reply #2 on: May 29, 2020, 11:48:40 am »
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What aspect of the question is difficult for you?

What working out have you done so far?
I have tried using a two-way table but never get an answer that is one of the options.
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colline

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Re: help with prob question
« Reply #3 on: May 29, 2020, 12:32:55 pm »
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I have tried using a two-way table but never get an answer that is one of the options.

In addition to a two-way table, see how you can use the information that the two are independent.

Find Pr(A) and Pr(B) first. Since they are independent, then Pr(A) * Pr(B) = Pr(A and B). Hope this helps! :)

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a weaponized ikea chair

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Re: help with prob question
« Reply #4 on: May 29, 2020, 01:54:54 pm »
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In addition to a two-way table, see how you can use the information that the two are independent.

Find Pr(A) and Pr(B) first. Since they are independent, then Pr(A) * Pr(B) = Pr(A and B). Hope this helps! :)
Thank you! I was now able to figure it out!

Quick question: if they were not independent, rather they were dependant, could you use the rule Pr(A) * Pr(B) = Pr(A and B)?
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colline

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Re: help with prob question
« Reply #5 on: May 29, 2020, 03:23:54 pm »
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Thank you! I was now able to figure it out!

Quick question: if they were not independent, rather they were dependant, could you use the rule Pr(A) * Pr(B) = Pr(A and B)?

The formula only applies if they are independent, so no.

Edit (if you want to know why):

Independent suggests the two events A and B literally do not affect each other in any way. So for example the probability of A happening given that B is true [i.e. Pr(A|B)] is no different to the probability of just A [i.e. Pr(A)]. So we can say that:
Pr(A|B) = Pr(A) when the two are independent.

And we know that Pr(A|B) = Pr(A and B) / Pr(B). Using the independence formula, Pr(A and B) = Pr(A) * Pr (B), so we can rewrite it as Pr(A) * Pr(B) / Pr(B). The Pr(B) cancels out and you are left with Pr(A|B) = Pr(A) when A and B are independent.

I hope that makes sense!
« Last Edit: May 29, 2020, 03:34:02 pm by colline »

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