Question

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

Answer 1

One third of an unknown number is $\frac{1}{3} x$.  The word "of" means to multiply.  So if we add 20 to that, and it is equal to double the unknown (that is 2x), the equation looks like this: $20+ \frac{1}{3}x=2x$.  Start by multiplying everything by 3 to get rid of the fraction and get 60 + x = 6x.  Now subtract an x from both sides and get 60 = 5x and x = 12.  So the number is 12

Answer 2

1/3 of an unknown number is 1/3x.  The word "of" lets us know to multiply.  So if we add 20 to that, and it is equal to double x (that is 2x), the equation looks like this: 

1. Start by multiplying everything by 3 to get rid of the fraction and get 20 + 1/3x = 2x.
2. Now subtract an x from both sides and get 60 = 5x and x = 12. 
So the answer is 12