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Lesson 3: Elapsed time

# Time FAQ

## What do the different hands on a clock mean?

On a clock there are two hands. The start color #bc2612, start text, h, o, u, r, space, h, a, n, d, end text, end color #bc2612 is the shorter hand. The start color #0c7f99, start text, m, i, n, u, t, e, space, h, a, n, d, end text, end color #0c7f99 is the longer hand.
A clock with every hour labeled showing the short hand on the 5 and the long hand on the 12.

## How do I read a clock?

First, we need to look at the hour hand. The hour hand is between 1 and 2, so it is after 1 o'clock but not yet 2 o'clock.
A clock with every hour labeled and tick marks every 1 minute. The short hand is between the 1 and 2. A line extends through the short hand to further show that the short hand is between the 1 and 2. The long hand is on the second tick mark after the 6.
So, the hour is 1. Next, we look at the minute hand.
The minute hand starts pointing straight up for 0 minutes.
When counting minutes, the distance between each tick mark represents 1 minute.
A clock with every hour labeled showing both hands on the 12. The minutes are labeled every 5 minutes around the outside of the clock as follows: 0 minutes is at the 12, 5 minutes is at the 1, 10 minutes is at the 2, 15 minutes is at the 3, 20 minutes is at the 4, 25 minutes is at the 5, 30 minutes is at the 6, 35 minutes is at the 7, 40 minutes is at the 8, 45 minutes is at the 9, 50 minutes is at the 10, and 55 minutes is at the 11.
Each number on the clock represents 5 minutes, with a total of start color #0c7f99, 60, end color #0c7f99 minutes in each hour.

## How can a number line help us find elapsed time?

If we unroll a clock, it becomes a number line! We can set up a number line to represent minutes in an hour. Then, we can mark the start time and end time of an event, and count the number of minutes between the two marks.
To find out how many minutes are between start color #208170, 9, colon, 18, end color #208170 to start color #bc2612, 9, colon, 57, end color #bc2612, we can find the distance from start color #208170, 9, colon, 18, end color #208170 to start color #bc2612, 9, colon, 57, end color #bc2612.
A number line labeled 9:15 to 10:00 with tick marks every 1 unit. A series of three arrows are shown moving left to right from the 9:18 tick mark to the 9:57 tick mark. The first arrow starts at the 9:18 tick mark and ends at the 9:20 tick mark and is labeled plus 2. The second arrow starts at the 9:20 tick mark and ends at the 9:50 tick mark and is labeled plus 30. The third arrow starts at the 9:50 tick mark and ends at the 9:57 tick mark and is labeled plus 7.
\begin{aligned} \tealE{9{:}18} +{} &\purpleD{2}\text{ minutes} = 9{:}20\\\\ 9{:}20 +{} & \goldE{30}\text{ minutes} = 9{:}50 \\\\ 9{:}50 +{}&\blueE{7}\text{ minutes} = \redE{9{:}57} \end{aligned}

## Why do we need to know how to calculate elapsed time?

Knowing how to calculate elapsed time helps us understand how long it takes to do certain things, like driving to a new place or completing a task.

## How can we use what we learned in this unit in the real world?

Time is an important part of our lives, so this unit has many real-world applications. We can use what we learned to keep appointments, plan our day, and understand how long things take.