Yahoo Answers is shutting down on May 4th, 2021 (Eastern Time) and beginning April 20th, 2021 (Eastern Time) the Yahoo Answers website will be in read-only mode. **There will be no changes to other Yahoo properties or services, or your Yahoo account.** You can find more information about the Yahoo Answers shutdown and how to download your data on this help page.

## Trending News

# Probability Math ?

I need help with 78 and 80.

### 1 Answer

- AlanLv 72 months agoFavorite Answer
Won't use there notation

n_C_k , I will write as C(n,k)

so both answers are hand feed to you

Just do the math

C(n,k) (p)^n (1-p)^(n-k) is the formula for all answers

C(n,k) = n! / ( k! (n-k)! )

so

78.

they tell you it gives you

C(10,3) (1/4)^3 (3/4)^7

C(10,3) = 10! / (3! 7!) = 10*9*8/ 3*2*1 = 10*9*4/3 = 10*3*4 = 120

C(10,3) (1/4)^3 (3/4)^7 = 120* ( 3^7/ 4^10) =

= 262440/ 1048576 = simplified 32805 / 131072

Exact answer 32805 / 131072

= approximate 0.250282288

80.

again , they tell you the answer is

C(8, 4) (1/2)^4 (1/2)^4

= C(8,4) (1/2^8)

= C(8,4) ( 1/256)

C(8,4) = 8!/ (4! 4!) = 8*7*6*5/ 4*3*2*1

8/(4*2) =1

6/3*1 = 2

C(8,4) = 7*2*5 = 14*5 = 70

=C(8,4) (1/256) = 70/256 = 35/ 128 =

exactly 35/128

approximately = 0.2734375