Question

The library states that 90% of books taken out of the library are returned before their due date. In a sample of 61 books, what is the probability that less than 80% were returned before their due date?

a) -2.60

b) 0.0047

c) 0.9953

d 0.1000

Answer 1

Solution

Given that,

p = 0.90

1 - p = 1-0.90=0.10

n = 61

= p =0.90

=  [p ( 1 - p ) / n] =   [(0.90*0.10) / 61 ] = 0.03841

P( <0.80 ) =

= P[( - ) / < (0.80-0.90) /0.03841 ]

= P(z <-2.60 )

Using z table,   

probability =0.0047