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## Class 8 (Foundation)

### Unit 6: Lesson 1

Ratio and proportion# Solving ratio problems with tables

We're displaying ratios in a table format here, and then asking: given a ratio, solve for equivalent ratios. Here are a few examples to practice on. Created by Sal Khan.

## Want to join the conversation?

- Could a triple number line work if you needed 3 lines !?.(42 votes)
- Most of number line need 2 lines, but there are some number lines have even 10+ lines.(1 vote)

- So we are adding or dividing?(9 votes)
- This is very hard(6 votes)
- What if you have
*54:3*and you need*36: ?*What if you have*?:5*?(3 votes)- The ratio 54:3 shows us that the simplified form is 18:1. This is because 54/3 = 18. Let's just call the blank part x. To find 36: x, you have to divide 36 by 18 to get 2 (so the ratio is 36:2). To find x:5, you have to multiply 18*5, which is 90 (the ratio is 90:5)

Hope this helps! :)(6 votes)

- The simple trick that I learned was that find the simplest form of the ratio and then answer the questions.(5 votes)
- Here is a problem:

The ratio of the distance Sam walked on Monday to the distance he walked on Tuesday is 7:5. How many times the distance that he walked on Tuesday is the distance he walked on Monday?

The answer is 1 2/5

I don't understand the problem and why this is the answer?

Could someone please Help.(3 votes)- No, I won’t cause my teacher’s watching.(3 votes)

- Do we multiply or divide?(3 votes)
- I am still confused maybe the net vid will help(3 votes)
- How come increasing by one is not a equivalent ratio?(2 votes)
- Are you asking if 1/2 and (1+1)/(2+1)=2/3 are the same?(2 votes)

- Is anyone being forced to do this at school?(2 votes)

## Video transcript

We're told this table shows
equivalent ratios to 24 to 40. Fill in the missing values. And they write the ratio
24 to 40 right over here. 24-- when the numerator is
24, the denominator is 40. So in that way, you
could think of 24/40. But then they want us to
write equivalent ratios where we have to fill
in different blanks over here-- here
in the denominator and here in the numerator. And there's a bunch of ways that
we could actually tackle this. But maybe the easiest is
to start with the ratio that they gave us,
where they gave us both the numerator
and the denominator, and then move from there. So for example, if we look
at this one right over here, the numerator is 12. It is half of the 24. So the denominator is also going
to be half of the denominator here. It's going to be half of 40. So we could stick a
20 right over there. And then we could go up here. If you compare the 3 to
the 12, to go from 12 to 3, you have to divide by 4. So in the numerator,
you're dividing by 4. So in the denominator, you
also want to divide by 4. So 20 divided by 4 is 5. And then we have
one more to fill in, this numerator right over here. And we see from the denominator,
we doubled the denominator. We went from 40 to 80. So we would double
the numerator as well, and so you would get 48. And what we just did here is we
wrote four equivalent ratios. The ratio 3 to 5 or 3/5 is
the same thing as 12 to 20, is the same thing as 24 to 40,
is the same thing as 48 to 80. Let's make sure we
got the right answer. Let's do a couple more of these. The following table shows
equivalent fractions to 27/75. So then they wrote all of the
different equivalent fractions. This table shows ratios
equivalent to 18/55. Fair enough. All right, so these are
all equivalent to 27/75. These are all equivalent
to 18/55, so all of these. Which fraction is
greater, 27/75 or 18/55? So this is an interesting thing. What we want to do-- because
you look at these two things. And you're like,
well, I don't know. Their denominators
are different. How do I compare them? And the best way that I
can think of comparing them is look at a point where you're
getting an equivalent fraction. And either the numerators
are going to be the same, or the denominators are
going to be the same. So let's see if there's
any situation here. So you have this situation
where we see 27/75 is 54/150. And over here, we see
that 18/55 is 54-- and this 54 jumped
out at me because it's the same numerator-- over 165. And that makes the
comparison much easier. What is smaller? 54/150 or 54/165? Well, if you have
the same numerator, having a larger denominator
will make the number smaller. So 54/165 is smaller than
54/150, which tells us that 18/55 is
smaller than 27/75. So let's see, which of these? So this is saying that
27/75 is greater than 18/55, and that is absolutely right. And let's do one more of these. Lunara's friends
are running a race. Each of them runs at a constant
speed starting at time 0. Which of these tables might
show the distances one of Lunara's friends
traveled over time? So they're running a race. Each of them runs at a constant
speed starting at time 0. So table 1-- so
distance run in meters. So they're running
at a constant speed. So really, the ratio
between distance and time should be constant throughout
all of these possible tables. So here you have
a ratio of 3 to 2. If you triple the distance,
we're tripling the time. If you multiply
the distance by 5, we're multiplying the time by 5. So table 1 seems
completely reasonable. Let's keep going. Table 2-- 11 to 4
and then 12 to 5. Here, it's just
incrementing by 1, but the ratios are not the same. 11 to 4 is not the
same thing as 12 to 5. So we're not going to be able
to-- this right over here is not a legitimate table. Table 3-- so 1 to 1. Then when you double the
distance, we double the time. When you triple the
distance from 1, you didn't triple the time. So table 3 doesn't seem
to make sense, either. Table 4-- so 14 to 10. So that's the same
thing as-- let's see, that's the same ratio as, if
we were to divide by 2, as 7 to 5 ratio. If we divide both of these by
3, this is also a 7 to 5 ratio. And if you divide both of these
by 7, this is also a 7 to 5 ratio. So table 4 seems like a
completely reasonable scenario. And we can check our
answer, and it is.