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## Grade 7 (Virginia)

### Course: Grade 7 (Virginia) > Unit 4

Lesson 5: Visualizing percents# Finding percentages with a double number line

Given the whole, use a double number line to reason about the percentage of the whole that another value represents. Created by Sal Khan.

## Want to join the conversation?

- how I can improve my math's skill?(6 votes)
- it does not (sadly)(2 votes)

- This is so confusing(11 votes)
- I know right!?(3 votes)

- How do you find an answer if you don't have a clue to it?(4 votes)
- If you don't know then you could re-watch or something different.(3 votes)

- 1:20Couldnt you just turn 21/28 into 3/4 then 3/4 into 75%?(3 votes)
- Indeed, but I think Sal purposefully showed us how to use the double number line(2 votes)

- wow new content!(3 votes)
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⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⢀⣄⠀⠀⠀⣸⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⠁⣠⡄⠀⣿⢹⡇⢸⡀⠀⠈⠻⢿⣿⣿⣿⣿⣿⣿(2 votes) - i dont understand cuz cant u just turn the number dirrectly into a percent? (sorry for bad grammer lol)(2 votes)
- one of my math questions is hard.Can someone help me. If you can please respond. The question is x3+y3+z3=k. Please help me.(1 vote)
- So when i watch the video's, normally they aren't very related to what i'm working with and it confuses me so bad, because the help box tell's me " here, watch this video" and it doesn't help, and also i cant replay the video's.(1 vote)
- This doesn't make much sense to me. Does anyone have a better explanation pls?(1 vote)

## Video transcript

- [Instructor] We're
told that Omar's class has 28 students in it. 21 of them take the bus to school. What percentage of the
students in Omar's class take the bus to school? Pause this video, and see
if you can figure that out. All right, well, I'm going
to try to visualize this with what we call a double number line. So let's say that is zero, and 28 is the total number of students in this classroom right over here. As a double number line, because I'm going to
make another number line right below it. But I'm going to write these
points in terms of percentages. So zero students would be 0% of the students in Omar's class, and 28 students would be 100% of the students in Omar's class. And so what we really need to do now is, we know that 21 of them take the bus. 21 is going to be roughly around here. So that's 21. So we really just need to figure out, is what percentage is this going to be? One way to think about it is
what fraction is 21 of 28? Well, if I write 21 over 28, we know that we can
divide both the numerator and the denominator by seven, they're both divisible by seven, 21 divided by seven is three, and 28 divided by seven is four. So 21 is three-fourths of 28. So let's divide this number line from zero to 28 into fourths. So that would be halfway, and now we have it divided into fourths, and we can see that 21 is one,
two, three of these fourths. Well, if 21 is three-fourths
of the way to 28, then whatever percentage this is here, that would be three-fourths
of the way to 100. So let's divide this into fourths as well. Now we know that one-fourth of 100 is 25%. Two-fourths of 100 is 50%. Three-fourths of 100 is 75%. So what percentage of the
students in Omar's class take the bus to school? 75%.