Questions and Answers

Question posted by Alicia from Singapore:

X is a whole number which lies between 50 and 150. It has a factor of 24. When X is divided by 9, its remainder is 3. What is X?


It is easier to solve the question using the "Listing Method", i.e., we make a list of the possible answers within the specified range.

Step 1: List all the multiples of 24 between 50 and 150 (There are only 4 possible values).

24: 72, 96, 120, 144

Step 2: Make a second list below the first by subtracting each number in the first list by 3.

24: 72, 96, 120, 144
-3: 69, 93, 117, 141

From the second list, we know that 69 and 93 are not the answers as they are not divisible by 9 (based on the child's knowledge of multiplication tables). We only need to divide the last 2 numbers (117 and 141) by 9 to determine which is the one that is divisible by 9.

Thus, we found that the number X is 120 (It has a factor of 24 and when divided by 9 leaves a remainder of 3).