Main content

# Time on a number line

Sal tells time on a number line. Created by Sal Khan.

## Want to join the conversation?

- why do we need a number line?(12 votes)
- It tends to be easier for some people to understand simple counting with a number line.(13 votes)

- Isn’t A Timeline like when event’s happen?(Like for e.x. The timeline of Jackie Robinson )(8 votes)
- It's like a number line but on the tick marks are dates that show when important events happen.(4 votes)

- How can we tell time?(3 votes)
- Count the interval from a known time.

So let's take the video's example.

Since the nearest (and below the current time) is1:15, and we count the interval between A and1:15, which is 10. Therefore, the time is1:15+0:10=1:25

I have created a tool to represent current time on a number line. You may want to check it out:

https://www.khanacademy.org/computer-programming/time-on-a-number-line/6673227777228800(2 votes)

- why is every line minutes and hours?(0 votes)
- That's just how this question is. Every line in this question is time because that's what the question is. However, not all number lines are time-related.(2 votes)

## Video transcript

- [Instructor] We're told to look at the following number line. In this number line, we
actually have times on it, so you could even call it a timeline. We're starting at one o'clock here. Then we go to 1:15, 1:30,
1:45, then two o'clock. And it says, what time is
shown on the number line? So, pause this video and see
if you can figure that out. All right, so the hour I think
is pretty straightforward. We are past one o'clock but
we are before two o'clock. So, we know that the hour is
going to be one something. It's not going to be two something 'cause we haven't gotten
to two o'clock yet. Now, what is the number of
minutes after one o'clock? Well, we have a hint here. It's going to be between 15 and 30. And where would it be? Well, one way to tell is if you look at each of these tick marks, it looks like they represent a minute. Let's just count. If we start at one, we go to 1:01, two, three, four, five, six, seven, eight, nine, 10, 11, 12, 13, 14, 15. Yep, it looks like each of
these tick marks is a minute. So, we just have to figure out how many tick marks we are past 1:15. So, we can see that we
can go from 15 to 16, 17, 18, 19, 20, 21, 22, 23, 24, 25. So, we're 25 minutes past one o'clock. Another way you could
have thought about it is each of these medium tick
marks represent five minutes. And you can count, one,
two, three, four, five. So, that's five, that's another five. So, this time right over here is going to be five plus five is 10, it's going to be 10 minutes past 1:15. Well, 15 plus 10 is 25 again. So, the time shown on
the number line 1:25.