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# Probability Math ?

I need help with 78 and 80. ### 1 Answer

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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

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