What is the smallest number which when decreased by 7 is exactly divisible by 12, 16, 18, 21 and 28?

The correct option is A 1015
To find the number, we will first need to find the LCM of 12, 16, 18, 21 and 28.

L.C.M = 2 $\times$ 2 $\times$ 2 $\times$ 2 $\times$ 3 $\times$ 3$\times$ 7
= 1008
Next add 7 to the LCM calculated to get the required number.

$\therefore$ The required number = 1008 + 7
= 1015
This number when decreased by 7 will be divisible by 12, 16, 18, 21 and 28