UNIT 1: CHAPTER 1- RATIO

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

Ratios can be shown in different ways:

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:		3 1

A ratio can be scaled up:

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 2/3     The 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 2/5     The ratio of girls to all pups is 3:5 or 3/5