Question

The average comic book has 55 pages and a standard deviation of 7 pages. Assume it has a normally distributed.

a) If a single comic book is selected, find the probability that the number of pages will be greater than 73.

b) If 25 comic books are selected, find the probability that the that the number of pages will be greater than 73.

Answer 1

Solution :

Given that,

mean = = 55

standard deviation = =7

(A)P(x > 73) = 1 - P(x<73 )

= 1 - P[(x -) / < (73-55) /7 ]

= 1 - P(z <2.57 )

Using z table

= 1 -  0.9949

probability= 0.0051

(B)

n=25

= =55

= / n = 7 / 25 = 1.4

P( >73 ) = 1 - P( <73 )

= 1 - P[( - ) / < (73-55) / 1.4]

= 1 - P(z < 12.86)

Using z table

= 1 - 1

= 0

probability= 0