Mentor: Consider the problem from before: "We started our math lesson at 10 a.m. It is now 11 a.m.
How long have we been doing math?"
Student: 1 hour.
Mentor: Right, and the fancy name for the time that has passed is
elapsed time. How do we figure out the elapsed time in a problem like that?
Student: I just subtracted: 11-10=1 hour.
Mentor: That's a really good method. Look at this problem: "If it's 1 p.m. now and I got to school at
8 a.m., how long have I been at school?" How would solve a problem like that?
Student: I would probably just count. 1 hour until 9, 2 hours until 10, 3 hours until 11, 4 hours
until 12, 5 hours until 1. 5 hours.
Mentor: Those are both really good methods of solving problems, but you can't forget that there are
sometimes minutes as well as hours in these problems. Try this one: "If you started eating
lunch at 11:45 and finished at 12:05, how much time is that?"
Student: I would solve that problem by adding the minutes. 15 minutes to 12:00, and 5 more minutes to
12:05. That's 20 minutes total.
Mentor: Great! Can you think of another way to solve it?
Student: You could subtract.
Mentor: How can you subract. You can't borrow like you normally would.
Student: You could take 1 hour and turn it into minutes. That would give you 11 hours and 60+5
minutes, 65. Then you subtract: 65-45=20 minutes. And 11-11=0 hours. So the answer is 20
Mentor: Great job! Now you're ready for some really tricky problems.