Mathematics - Probability Question with Solution | TestHub

Each coupon can be selected in 15 ways. The total number of ways of choosing 7 copouns is $15^7$. If largest number is 9 , then the selected numbers have to be from 1 to 9 excluding those consisting of only 1 to 8. Probability desired is $\frac{9^7-8^7}{15^7}$ $={\left(\frac{3}{5}\right)}^7-{\left(\frac{8}{15}\right)}^7$