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Lesson 1: Ratio

# Intro to ratios

The video explains ratios, which show the relationship between two quantities. Using apples and oranges as an example, it demonstrates how to calculate and reduce ratios (6:9 to 2:3) and how to reverse the ratio (9:6 to 3:2). Created by Sal Khan.

## Want to join the conversation?

• How are ratios used in real world problems?
• Say you have a job as a store employee and your stocking shelves and your boss wants each item to have the same amount as the item next to it. In a quick summary she/he wants you to tell them how much is in each one. You'd count the amount of items in each one and state a ratio.
• What is a ratio?
• Let's say you have to come up with a ratio to show the relationship between red and green mushrooms from this problem:

There are 6 red mushrooms and 3 green mushrooms in a bag.

There are obviously 6 red mushrooms for every 3 green, so you could write a ratio like this:
6:3 or 6/3 or "6 to 3."
You can treat a ratio just like a fraction (which is why you can also write it like one: 6/3), so you can reduce 6/3 to 2/1.
So in that original bag, there are 2 red mushrooms for every 1 green mushrooms.
Ratios have lots of other uses as well, but I think this will give you a basic idea. Keep watching the videos.
• why do we use ratios if we already have fractions
• People in this world use fractions to show how much of a whole they are talking about. For example, 5/7 would mean 5 out of seven things. Ratios are used to to express how much of 2 or more things are required to make a whole. This can be simplified, for example, instead of saying , I could say 5:4.

You might be saying that you can do the same thing with fractions, which is true. However, in the case of fractions, the numerator is only one number, and it tells only how much of ONE thing is needed out of a whole, and in ratios, it tells you how much of 2 THINGS are required to make a whole.

• So, a ratio is the amount of each object in each group?
• Ratio is more about the relationship between two numbers rather than the value of an object per group. Ratio can also be shown as a form of fractions (6:9 means 6 per 9, or 6/9) and division (6 divided by 9). So, to answer your question, ratio is about how much of something there is, but the main definition is about "how much there is something compared to another" or "the amount of something per something else".

Hope this helps!
• Do the ratio numbers have to begin with the number that is explained first? I dont understand, someone please help me out.
• yes for example what is the ratio from pears to apples you are going to do peas first then apples
• how can YOU SIMPLIFY ?
• you cant simplify that because it does not have anything in common
• really how are ratios used in real world problems and where at in the world like i don't understand like where
• It's often a statistics sort of thing, but it can be used for any situation that you want to report two values.

Stores= 4 apples to 3 dollars === 4:3
House listings= 4 bed to 1 bath === 4:1
School stats= 50 students to 1 teacher === 50:1

All those show a relation of one thing to another so that people can make decisions.
"75 cents per apple is too expensive! I won't buy it!"
"4 bedrooms and we all need to share a bathroom? Ew, no."
"50 kids per one classroom!? We need more teachers!"
• When will we ever need to use ratios for real life conflicts?
• It may seem silly, but ratios can be used for everyday purposes, such as cooking.