The box contains tickets numbered from 1 to 20. Three tickets are drawn from the box with replacement. The probability that the largest number on the tickets is 7 is a. `2//19` b. `7//20` c. `1-(7//20)^3` d. none of these

Answer

D

Explanation

Let X denote the largest number on the 3 sticks drawn. Then, `P(Xle7)=(7//20)^(3)and P(Xle6)=(6//20)^(3).` Then, the required probability is
`P(X=7)=((7)/(20))^(3)-((6)/(20))^(3)`