A bus takes (9) passengers at the first stop and (3) more passengers board at each next stop. How many passengers board at the (9)th stop?

Correct answer: 33

This is an arithmetic progression with first term \(a=9\), common difference \(d=3\), and term number \(n=9\). Thus, \(a_9=a+(n-1)d=9+(9-1)\times3=33\). Therefore, 33 passengers board at the 9th stop. Option 36 results from adding 3 nine times, but there are only 8 increases from the first stop to the ninth stop. Exam tip: use \(n-1\) differences when finding the \(n\)th term of an AP.