Main content

## SAT (Fall 2023)

### Course: SAT (Fall 2023) > Unit 10

Lesson 3: Problem solving and data analysis- Ratios, rates, and proportions — Basic example
- Ratios, rates, and proportions — Harder example
- Percents — Basic example
- Percents — Harder example
- Units — Basic example
- Units — Harder example
- Table data — Basic example
- Table data — Harder example
- Scatterplots — Basic example
- Scatterplots — Harder example
- Key features of graphs — Basic example
- Key features of graphs — Harder example
- Linear and exponential growth — Basic example
- Linear and exponential growth — Harder example
- Data inferences — Basic example
- Data inferences — Harder example
- Center, spread, and shape of distributions — Basic example
- Center, spread, and shape of distributions — Harder example
- Data collection and conclusions — Basic example
- Data collection and conclusions — Harder example

© 2023 Khan AcademyTerms of usePrivacy PolicyCookie Notice

# Ratios, rates, and proportions — Harder example

Watch Sal work through a harder Ratios, rates, and proportions problem.

## Want to join the conversation?

- I am seriously losing hope as I watch more complex videos and do more complex math problems(67 votes)
- So, real quick... without writing and quickly using your head (not a calculator) you can figure out this one!

To make this easier to see, simply take his ratio in the problem (1cm = 20ft) and square it out. Yes, he did this, but wrote a lot. All you need to write down during the test is basically the 20 (if you need to see it to remember it is there). It is 400 because 2 squared is 4 (then put the zeros back in place to make it 400)

Next, we already see that 400 square feet is what 1 pound will cover. Under the entire field, there are 180 sections of 400 square feet. that's 180lbs. Done and only 5 seconds out of your 55 minutes (or whatever section this is in)! 😊

If you have a mind for patterns, ratios, rates and proportions are easy. But if not, that's ok because often times you will have the tendency to be able to handle many more types of problems I will never be able to ever figure out! 😉(71 votes)

- this question is troubling me:

There are 78 biscuits in a box. Some are salty and the rest are sweet. Which of the following could be the ratio of salty to sweet biscuits in the box?

A) 3:4 B) 4:1 C)5:11D) 5:8 E) 1:3(10 votes)- E has to be the answer. Unless the biscuits are broken and you are considering bits of pieces of biscuits, the only number in the given options that divides 78 perfectly is the number 3. For example 78/3=26. However, 78/4=19.5 and since there aren't half biscuits when considering ratios of salty and sweet biscuits, all answers with 4 is wrong eliminating A, and B. C is not the answer because both 5 and 11 does not result in an integer. 78/5=15.6 and 78/11=7.09 eliminating C, thus since D has 5 as well, it cannot be the answer. Also the 8 in D results in a 9.75 which does not make sense. Therefore, the only reasonable answer is E containing 1 and 3, both resulting in a integer when dividing 78.(17 votes)

- how is one minute enough to answer this on the sat? The hardest part isn't solving it. The hardest part is just trying to understand what that question is asking of you.(24 votes)
- It took like 10 sec to solve this..(8 votes)

- For this question, instead of doing all that work to get 180 pounds, wouldn't have it been much simpler to realize that for every square centimeter, it is 400 square feet, and for every 400 square feet, it's one pound of seed, so then you would need 180 pounds of seed?(27 votes)
- Dam I guess everyone thought it was 9(18 votes)
- Guys i'm new here

right now i just need some encouraging words

i'm beginning to loose hope on sat(16 votes) - Will they give you the conversions on the SAT or will we have to memorize the actual conversations?(7 votes)
- I think they usually provide the conversions in parenthesis. The only thing I think you would have to know is time. For examples, 60 seconds in a minute and 60 minutes in an hour.(8 votes)

- i thought the answer would be 9 since x= number of pounds of seed she need to cover the entire field 3600/x=400/1 400x=3600 x=9pounds(10 votes)
- your mistake is in the conversion of the units :

if 1cm=20ft you cannot convert 180cm^2 to ft^2 by simply replacing cm with 20ft then doing 180*20=3600

and that's because 1cm is different than 1cm^2

if 1cm=20ft

1cm^2=400ft^2

which means that 180cm^2=72 000ft^2(not 3600)

NOW if you try your method:

72000/x = 400/1

400x = 72000

x = 72000/400 = 180(1 vote)

- not going to lie but when I read the question before he solved anything I thought the answer was 9 because I divided 180 by 20 and after he solved it it made much more sense because, with my answer, the field would be small compared to the right answer.(8 votes)
- Hi guys. Do u know which sections in the SAT allow to use calculator ?(5 votes)
- You are allowed to use a calculator in a specific section of math.(3 votes)

## Video transcript

- [Instructor] Erika
plans to purchase seed to plant grass in a large field. She has a map of the region, and calculates the area
of the region on paper to be 180 square centimeters. The scale on the map shows that one centimeter is equal to 20 feet. So they're giving us linear
centimeters to linear feet, not square centimeters to square feet, so I think we're gonna
have to figure that out. If Erika plans to cover
every 400 square feet with one pound of seed,
approximately how many pounds of seed will she need to
cover the entire field? So what we wanna do is
we wanna figure out, well, how many square feet is the field? How many square feet is the field? And we know on her map, her map has, well, a map of the field, and she's, on the map it's
180 square centimeters. And they tell them or they tell us that one centimeter is equal to 20 feet. But if this is square centimeters, then we wanna convert this to square feet. So to convert, if one
centimeter's equal to 20 feet, to convert it from, if we
wanna figure out the conversion from square centimeters to square feet, we could just square both sides of this. We could just square both sides of this. And what will that be? One squared is still one, but now we have one centimeter squared. And I could write it like
this just to be clear that I took both of them
to the second power, but one squared is just one. And this is going to be equal, 20 squared is going to be 400 square feet. So one square centimeter
on this map is going to be equal to 400 square feet. So how many square feet does 180 square centimeters represent? So I could write 180 centimeters squared. And we know that every centimeter squared represents 400 feet, or we
could say 400 feet squared per centimeter squared. And we want the units to cancel
out, so this makes sense. You have centimeters squared
over centimeters squared. So the actual field is going to be 180. 180 times 400. Times 400 square feet. And that makes sense. The region on paper was
180 square centimeters. Each square centimeter is equal to 400 square feet in reality. So for each of those square centimeters, it's going to be 400 square feet. So it's 180 times 400. So this is the area in square
footage of the actual field, and then they tell us we're
gonna use one pound of seed. One pound of seed for
every 400 square feet. So let's see, the area
of the entire field, let me give myself a
little bit more space, is, and I'm not gonna even multiply it out because this 400 is showing
up, so this seems useful. So the area is 400 feet squared. I just wrote that. And we're going to use one pound, one pound of seed, pound of seed, for every 400 square feet. For every 400 square feet. And if we look at it,
the units cancel out. Square feet divided by square feet. Then we have 400 divided by 400. And we're left with 180
times one pound of seed, which tells us that we're
going to use 180 pounds, 180 pounds of, 180 pounds of seed, which is that choice right over there. Now, if you're under
time pressure on the SAT, although I would be careful, because this one is a little bit, it could be a little confusing. But you might've said, okay,
there's 180 square centimeters. Each of those square
centimeters is 400 feet. This is actually the key thing
that you have to realize, that each square centimeter
is not just 20 feet. It's 400. It's 400 feet. So you're gonna have 180
times 400 square feet for the entire field. But then each of those 400 feet, each of those 180 400 square feet, you're gonna use one pound of seed. You're gonna use 180 pounds of seed. So you could've done it
without all of this writing, but it is helpful to write it so that you don't confuse things.