The gas tank of Mr. Tanaka's car holds 15 gallons of gas. He used 2/3 of a tank of gas last week. How many gallons of gas did Mr. Tanaka use?

Mr Tanaka used 10 gallons of gas. You find this answer by diving the denominator (3) with the total number of gallons of gas. So 15 divided by 3 is 5. Now you get the number 5, and multiply it by the numerator (2). 5*2 is 10. That is how you find the answer.

15gallons * (2/3) = 10.