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?

15gallons * (2/3) = 10.

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.