A) three numbers sum to 15. the mode of the three numbers is 1. what must the three number be?
and
b) three numbers have a mode of 5 and a total of 11.what is the range of the three numbers?

The mode is a number that is repeated the most, so if there is 3 numbers, the "mode number" has to be repeated twice or three times. 

A)  since 1 is the mode, two of the numbers are 1, the last number is
15 -1 -1 = 13   the three numbers are 1, 1, and 13.

B)  since 5 is the mode, two of the numbers are 5, the last number is
11 -5 -5 = 1   the three numbers are 5, 5, and 1.

Range is when you subtract the smallest number to the biggest number, so 5-1=4  The answer is 4