Elapsed Time

1. Elapsed Time Objectives: I can tell time on an analog clock and represent the time in writing. I can use a number line to represent the hours and minutes of a clock, and use it to solve elapsed time problems.

2. Review In previous grades, you should have learned to tell time on an analog clock. We know that the short hand is the hour hand, and the long hand is the minute hand. The number that the short hand is pointing to tells the hour. On the face of the clock, there are 12 hours. In a day, though, there are 24 hours. That is why we use AM (before noon) or PM (after noon) to tell the difference between 6 in the morning (AM) and 6 in the evening (PM). Please tell me you remember what noon is… For the minute hand, we need to pay close attention to the notches on the clock. There are “little” notches, and “big” notches. How many minutes does the first big notch represent? And each little notch? You probably already know how many minutes are in an hour, but to review, let’s just count by 5s as I point to each big notch around the clock. So according to this clock, what time is it?

3. Review When we write time, we need to make sure we separate the hours and the minutes so that we don’t confuse the two. Here is how we do it: Hours  12:07  Minutes Colon to separate the two. So, how would you write the time being displayed by the clock here? Let’s do a couple really quick review questions!

4. Review What time is represented by this clock? What time is represented by this clock? We will probably need to do this as a class, but, how much time elapsed between the two clocks?

5. Using a Number Line You might notice that a clock is like a number line. If you were to “cut” the number line right at 12, you could roll it out into a straight line. Here is what 1 hour would look like on a number line: How should I fill in the “little” notches? 0 5 10 15 20 25 30 35 40 45 50 55 60 12:00 1:00

6. Solving Word Problems We can even use a number line to solve word problems involving time. Here is one: 1. Ms. Harris went to a baseball game at 2:10. At 2:30 she got hit in the head by a home run ball and had to go home. How long was she at the game? First, I want to plot the starting time. What was the starting time? Next, I want to plot the ending time. What was the ending time? Now, I need to figure out how much time elapsed between the starting time and the ending time. We can skip count up to figure it out. 0 5 10 15 20 25 30 35 40 45 50 55 60 2:00 3:00

7. Solving Word Problems Sometimes a problem gives us the start time, and the elapsed time, but we need to figure out the end time. Let’s try one… 1. Ms. Harris went to a baseball game at 2:07. She stayed at the game until she got hit in the head by a home run ball 13 minutes later. What time did she get hit in the head? First, I want to plot the starting time. What was the starting time? Next, I want to count up 13 minutes. Now, I need to determine the ending time. 0 5 10 15 20 25 30 35 40 45 50 55 60 2:00 3:00

8. Solving Word Problems We can even use a number line to figure out problems that go beyond an hour. 1. Mr. Superawesomeshige was playing baseball. He started playing at 1:55. At 2:13, he hit a home run that ended up hitting a fan in the head. How long was Mr. Superawesomeshige playing baseball until he hit a home run? 0 5 10 15 20 25 30 35 40 45 50 55 60 5 10 15 20 25 30 35 40 45 50 55 60 1:00 2:00 3:00

9. Left Side Construct a number line and solve the following problems on the left side. Jimmy John left his home at 3:15. He rode his bike to work and arrived at work at 3:50. How long did it take him to get to work? McDonald, the King of Burgerland, started cooking at 2:36. He cooked for 30 minutes. What time did he finish cooking? Challenge: 3. A stone started rolling down a hill at 1:45. It rolled for 25 minutes before it landed in a river. The river carried the stone downstream for another 50 minutes until it got stuck between a rock and a hard place. At what time did the stone land in the river? At what time did the stone stop traveling?