[Question]: Harper has 15 rubber bands. His brother has 6 fewer rubber bands than he has. How many rubber bands do they have together?
[Answer]: His brother has 15 rubber bands - 6 rubber bands = 9 rubber bands. They have 15 rubber bands + 9 rubber bands = 24 rubber bands together.
So the answer is 24.

[Question]: The trip from Philip's house to the children's school is 2.5 miles, and the trip to the market is 2 miles. He makes the round trip to school two times (when taking the children to school and when bringing them back) every day for 4 days a week. Then he makes a round trip to the market once during weekends. What is his car's mileage for a typical week?
[Answer]: Making the round trip to school means driving from the house to school and then back, for a total of 2.5 + 2.5 = 5 miles. He makes this trip twice in one day for a total of 2 * 5 = 10 miles. He does this 4 times in a week for a total of 4 * 10 = 40 miles. The round trip (once a week) to the market is 2 + 2 = 4 miles. His total mileage for a typical week = 40 + 4 = 44 miles.
So the answer is 44.

[Question]: There are 20 boys and 11 girls in the second grade and twice that number in the third grade. How many students are in grades 2 and 3?
[Answer]:
There are 20 + 11 = 31 students in second grade. There are 31 x 2 = 62 students in third grade. In total, there are 31 + 62 = 93 students.
So the answer is 93.