Ratios in real life

Ever made lemonade that tasted way too sour? Or way too watery? The secret to getting it just right is a ratio.

A ratio compares two amounts. Our recipe uses two cups of lemon juice for every three cups of water. That's a part to part ratio: lemon juice to water, two to three.

You can write it three ways: two to three, two colon three, or two over three. Order matters! Lemon juice comes first, so it's not three to two.

A part to whole ratio compares one part with the total. Two plus three is five cups in all, so juice to total is two to five. Two fifths of the lemonade is lemon juice.

Now, it's party time! We need more lemonade that tastes exactly the same. Double the recipe: four cups of juice to six cups of water. Triple it: six to nine. Every glass is the very same color, because these are equivalent ratios.

But careful! Adding the same amount to both doesn't work. Add four cups to each, and you get six to seven. That's less water than six to nine, so it's too sour.

A double number line shows the same pattern. Juice goes on top, and water goes underneath. Every two cups of juice lines up with three cups of water.

Ratios help at the store, too. Four lemons cost two dollars. Divide both by four to find the unit rate: fifty cents per lemon. So ten lemons cost five dollars.

So, remember. A ratio compares two amounts, part to part or part to whole. Equivalent ratios multiply both parts by the same number. And a unit rate tells you the amount for just one.