Question

If 13 is added to a number and the sum is multiplied by 3, the result is 7

times the number decreased by 9. Find the number.

Answer 1

75

Explanation:

Let n stand-in for "number"

"If 13 is added to a number," so: n + 13

"and the sum is multiplied by three," so: 3(n+13)

"The result is," so: 3(n+13) =

"7 times the number decreased by 9," so: 3(n+13) = 7n - 9

Now you can simply by moving numbers across the equal sign:

3n + 39 = 7n - 9

39 = 4n - 9 (take 3n off from both sides)

48 = 4n (add 9 onto both sides)

12 = n

And then check:

3(12 + 13) = 7(12) - 9

3 x 25 = 7 x 12 - 9

75 = 84 - 9

84 - 9 = 75