if 20 is added to one-third of a number,the result is the double of the number. what is the number?

Question

 this is a year 8 problem solving question 

Answer 1

Let's say the number is called x.

 

So 1/3 x + 20 = 2x because 2x is the double of x.

Subtract 1/3 x from both sides: 20 = 2x - 1/3 x = 5/3 x

 

Multiply both sides 3, so we get 3*20 = 5x = 60, so x = 12