Find the sum of all the common multiples of 8 and 9 (upto 100). [2 marks]

Solutions:

Multiples of 8: 8, 16, 24, 32, 40, 48, 56, 64, 72, 80, 88, 96 [0.5 marks]
Multiples of 9: 9, 18, 27, 36, 45, 54, 63, 72, 81, 90, 99 [0.5 marks]

Common Multiples of 8 and 9 upto 100 are: 72

As there is only one common multiple, thus sum will be also be 72. [1 mark]