Prior Skills Needed: Students must know: there are 60 minutes in an hour, their ten combinations, and how to count by tens and hundreds.

Further they will need to know or be taught how to use a number line to solve difference (subtraction) problems which I will explain here.

To solve the problem 13-7, a student draws a line and writes 13 on the far right and 7 on the far left. From 7, the student draws line jumps to make 10, so the first jump is +3 to get to 10. The next jump the student wants to get to 13 so the final jump would be +3. Adding the two jumps, 3+3 is 6, which is the answer.

Here’s another 63-28. Draw a line with 63 on the far right and 28 on the far left. Starting at 28, make a 10 by adding 2. So, the first jump is +2 which brings you to 30. Second, count by tens. You are at 30 so you jump to 60 which is +30. Finally, the last jump is +3 ones to get to 63. Add the jumps together, 2+30+3, so the answer to the problem is 35.

Lastly, let’s add 100′s into the mix. Try your hand at 230-119. Draw your line, 230 on the right, 119 on the left. Start on the left, jump to the next 10 (+1 to 120). Jump to the next 100 you want (+100 to 220). Jump to the next 10 you want (+10 to 230). If there were ones, you might have to do a last jump. Add the jumps (+1+100+10=111). Your answer is 111.

Now, try elapsed time using the same method. Let’s solve the following story problem together:

Luìs got on the bus for a classroom astronomy field trip to the Observatory at 1:35p.m. After studying several charts of galaxies and nebulae inside and viewing Saturn’s rings through the telescopes outdoors, Luìs and his class got back on the bus and headed back to school. They arrived 2 minutes late at 5:02p.m. and got to have a pizza party before going home. How much time in-between when Luìs got on the bus at 1:35p.m. and when he arrived back at school at 5:02p.m.?

Draw a line. Write 5:02 on the far right side and 1:35 on the far left side. Start from 1:35 and jump to the next 10. (+5mins. to 1:40). Next, jump to the next hour, just remember that you’re not making 100 but 60 since there are 60 minutes in an hour, so instead of adding 40 and 60 to make 100, you want to add 40 and 20 to make 60 (+20mins. to 2:00). Next, jump by 1′s to the hour you want, be sure to label it in hours (+3hrs. to 5:00). Finally jump the remaining minutes (+2mins. to 5:02). Add up all your jumps (5mins + 20mins. + 3hrs. + 2mins.) Add the minutes and hours separately. You should get 3hrs. and 27mins. as your answer. Notice that you can challenge students to combine the first two steps in to one step and jump straight from 1:35 to the next 60 combination (35+25=60) which can be slightly more challenging. You may also present a problem where the minutes add up to larger than 60 and students will need to convert minutes to hours adding yet another level of challenge. Try several more on your own!

Did you notice how much detail I wrote into this story problem? Besides learning a new skill, the story part of the math problem is developed to engage the student’s sense of curiosity (using the astronomy vocabulary), their sense of meaning (class trip), and appeal to their sense of fun (pizza party). The student is likely excited and engaged and may want to discuss their recent trip or how much they love pizza or what they know about astronomy. STOP! Don’t tell them to be quiet and focus! (This will just make them focus on how they didn’t get to share their story). Let them talk, just give them some parameters. This is great discussion to warm up students’ brains and get them intrinsically motivated and excited to solve this problem. Tell them you will give them 2 minutes to talk to a friend or neighbor about how they can each relate to this problem. They may want to try more and more elapsed time problems and even make up their own stories!