The number of pupils must be 1 more than a common multiple of 3, 4, and 9.
Find the LCM of 3, 4, and 9, then add 1.
AGS Rule Box
LCM of 3, 4, 9=36 (since 36 is the smallest number divisible by 3, 4, and 9)
Total pupils=36 + 1 = 37
Final Answer: 37