Let's take the difference between the old and new (70 - 60) to get 10 and then divide this by the old (70) amount...10/70 = .142857 convert to a percent by moving the decimal 2 spaces to the right... 14.29 %
Assume that the other number is y. we know that the addition of both number is -9 this means that: x+y=-9 reorder this equation to seperate the y variable: y=-9-x
