Fifteen coupons are numbered 1, 2, 3, …. 15. Seven coupons are selected at random one at a time with replacement. The probability that the largest number appearing on the selected coupon is 9, is

none of these

Total ways = 15⁷

For favorable ways, we must 7 coupons numbered from 1 to 9 so that '9' is selected atleast once. Thus total number of favorable ways are, 9⁷ - 8⁷

⇒ Required probability = $\frac{9^7-8^7}{15^7}$