A 20 of the time 900 of these boxes of books will weigh a to

A) 20% of the time, 900 of these boxes of books will weigh a total of atleast how many pounds?

B) What is the probability that one randomly selected box of books wil weigh between 38 and 43 pounds?

C) What is the probability that the combined weight of 5 randomly selcted boxes of books will exceed 230 pounds?

(A)P(X<c)=0.2

--> P((X-mean)/s <(c-42)/7) = 0.2

--> P(Z<(c-42)/7) = 0.2

--> (c-42)/7= -0.84 (from standard normal table)

So c= 42-0.84*7= 36.12

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(B) P(38 <X< 43)

=P((38-42)/7 <Z< (43-42)/7)

=P(-0.57<Z<0.14)

=0.2713 (from standard normal table)

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(C) mean=42*5 = 210

standard deviation =7*5 =35

P(X>230) = P(Z>(230-210)/35)

=P(Z>0.57) =0.2843 (from standard normal table)