Math equation

Question

A student was asked to subtract three from a number and then divide that answer by nine. Instead, the stiudent mistakenly subtracted nine from the number and then divided the answer by three, getting a final result of 43. If the student had done the problem as instructed, what would have been the correct answer?

Answer 1

Define a variable:

Let x = number in question.

First the student subtracted 9 from the number in question, then divided the result by 3 and came up with the final result of 43.

 

So,

x - 9 was the first step.

then, 

(x - 9)/3 = 43

Solve for x:

(x - 9)/3 = 43

Multiply both sides by 3:

(x - 9) = 43 * 3

x - 9 = 129

Add 9 to both sides:

x = 138

 

The instruction was to subtract 3, then divide by 9, so the problem should be

(138 - 3)/9

135/9 = 15

The right answer would have been 15