Ratios
A ratio compares values.
A ratio says how much of one thing there is compared to another thing.
There are 3 blue squares to 1 yellow square
| Using the ":" to separate the values: | 3 : 1 | |
| Instead of the ":" we can use the word "to": | 3 to 1 | |
| Or write it like a fraction: | 31 |
Here the ratio is also 3 blue squares to 1 yellow square,
even though there are more squares.
Using Ratios
The trick with ratios is to always multiply or divide the numbers by the same value.Example:
| 4 : 5 is the same as 4×2 : 5×2 = 8 : 10 |  |
Recipes
Example: A Recipe for pancakes uses 3 cups of flour and 2 cups of milk.
So the ratio of flour to milk is 3 : 2
To make pancakes for a LOT of people we might need 4 times the quantity, so we multiply the numbers by 4:
3×4 : 2×4 = 12 : 8
In other words, 12 cups of flour and 8 cups of milk.The ratio is still the same, so the pancakes should be just as yummy.
"Part-to-Part" and "Part-to-Whole" Ratios
The examples so far have been "part-to-part" (comparing one part to another part).But a ratio can also show a part compared to the whole lot.
Example: There are 5 pups, 2 are boys, and 3 are girls
 |
Part-to-Part:
The ratio of boys to girls is 2:3 or 2/3The ratio of girls to boys is 3:2 or 3/2
Part-to-Whole:
The ratio of boys to all pups is 2:5 or 2/5The ratio of girls to all pups is 3:5 or 3/5 |
Try It Yourself
What is the ratio of oranges to strawberries? : 
What is the ratio of strawberries to oranges? :
What is the ratio of oranges to total fruit? :
What is the ratio of strawberries to total fruit? :
© 2015 MathsIsFun.com v0.91
Scaling
We can use ratios to scale drawings up or down (by multiplying or dividing).| The height to width ratio of the Indian Flag is 2:3 So for every 2 (inches, meters, whatever) of height there should be 3 of width. |
 |
If we made the flag 20 inches high, it should be 30 inches wide.
If we made the flag 40 cm high, it should be 60 cm wide
(which is still in the ratio 2:3)
| |
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