The first row of a theatre has (24) seats and each next row has (5) more seats. Which row will have (99) seats?

Correct answer: (16)

This forms an arithmetic progression with first term 24 and common difference 5. Therefore, the number of seats in the nth row is \(a_n=24+(n-1)\times5\). Setting \(24+(n-1)\times5=99\) gives \(5(n-1)=75\), so \(n=16\). Hence, the 16th row has 99 seats. The 15th row would have only 94 seats. Exam tip: for row-number questions, first write \(a_n=a+(n-1)d\).