The three numbers that make up the code to a safe sum 91. The last number is a multiple of 3, the middle number is 1/3 the last number, and the first is 3 times the last number. What is the middle nimber of the code?

7

Explanation:

Let the middle number be x.

Since the middle number is 1/3 the last number, then the last number has to be three times the middle number,

Therefore the last number is 3x

The first is 3 times the last number, meaning the first number has to be 3*3x=9x

All the three number add up to 91,

thus 9x+x+3x=91

13x=91

x=91/13=7