The average of the first five multiples of 12 is 36.

Explanation:

Multiples of a number are set of numbers which you get by multiplying that number with other numbers.

The first multiple of a number x is x, the second multiple is 2x, the third multiple is 3x and so on.

Thus first five multiples of 12 are

=> 12*1, 12*2, 12*3, 12*4, 12*5

=> 12, 24, 36, 48, 60

Now an average of these multiples = sum of multiples / number of multiples

=> Sum of multiples = 12 + 24 + 36 + 48 + 60 = 180

=> Number of multiples = 5

Average of first five multiples of 12 = 180/5 => 36