Math problem (Level 2) : Add 3 or 8 to a number (GG6)

There are numbers to become the multiple of 8 when I add 3, and those numbers becomes the multiple of 3 when I add 8.
What is the smallest number of them?

Answer

13

Solution

Such a number that becomes the multiple of 8 when I add 3 and becomes the multiple of 3 when I add 8, is the number should be the multiple both of 8 and 3 when I add 11(=3+8). 

It is the common multiple of 8 and 3. 

Then we can find the smallest number is 24 - 11 = 13 as the least common multiple of 8 and 3 is 24.