DAT Destroyer Math Problem

[researchlove]

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The policy says not to post the entire question, so I'm just going to refer it to the number (#64 in Math) which deals with probability..

it uses the equation:

P=(n C r)*(p)^n*(1-p)^r

obviously p is the probability of an event occurring,
n is the totalnumber of trials and
r is the number of trials having the desired result.

seems like n=3, and r=2 in the question, but the answer key substitutes 2,1 respectively to the equation above. Can someone explain this to me? 😕

 

[Shinpe]

The policy says not to post the entire question, so I'm just going to refer it to the number (#64 in Math) which deals with probability..

it uses the equation:

P=(n C r)*(p)^n*(1-p)^r

obviously p is the probability of an event occurring,
n is the totalnumber of trials and
r is the number of trials having the desired result.

seems like n=3, and r=2 in the question, but the answer key substitutes 2,1 respectively to the equation above. Can someone explain this to me? 😕

It's P^r * (1-p)^(n-r). n=3, r=2 => p^2*(1-=)^(3-2=1)