Question 451265
Three positive numbers, a, b, c
:
Bo took three positive numbers, subtracted the second from the first, and then subtracted the third from that difference.
a - b - c
:
Jo took the same three numbers in the same order, but subtracted the third from 
the second, then subtracted this difference from the first number. 
a - (b - c) 
a - b + c
:
If jo's result was 12 larger than bo's, what was the third number that they both used? 
bo's + 12 = jo's
a - b - c + 12 = a - b + c
combine like terms on the left
a - a - b + b - c - c + 12 = 0
-2c + 12 = 0
-2c = -12
2c = 12
c = 12/2
c = +6