A box has 20 paper slips having a number from 1-20 written on it. One slip is chosen at random from the box. The probability that the chosen slip has a composite number on it, is: 

$\frac{11}{20}$

According to problem 20 slips have 20 number between 1 to 20

So Exhaustive no. of case are = (1,2,3,4,5,...........................20) = 20

The composite no. between 1 to 20 are = (4,6,8,9,10,12,14,15,16,18,20) =11

So, The probability that a slip is chosen at random will have a composite no. on it P(E) =  11/20