After exams childrens throw their books how can they use them?

If those were work books that answers, I believe they should not throw them out.  They should keep them especially if the subjects are any type of math, chemistry or physics.  I recommend this because some of the questions in these books can come either in college or sometimes at a job exam.  They can use that as a reviewer. 

i used to know but i learned it a long time ago sorry

explanation:

the answer is sail boat won the race , and it was going 8 feet per   second