Ratios.

Step 1 of 5

Three times the recipe

A pancake batter: 200 g of flour for every 300 ml of milk. The ratio of flour to milk is $200 : 300$⁠. The board has two lines that start together at $0$⁠: flour on top and milk below, and every tick on the top line stands over the amount that goes with it on the bottom line. Each such pair of ticks is one more whole recipe.

Marker is locked at 600 g, three times the recipe. Predict how much milk it needs.

Step 2 of 5

Simplifying a ratio

A ratio does not change when you multiply or divide both its parts by the same number, just like a fraction. You can divide $200 : 300$⁠ to get a ratio in smaller numbers with exactly the same taste. A ratio that cannot be divided any further is in its simplest form.

Answer, then drag Look inside to check.

Step 3 of 5

Add or multiply?

A friend of yours made a bigger batter: he added 200 g of flour and 200 ml of milk, and ended up with 400 g of flour and 500 ml of milk. Marker stands at 400 g. Predict whether his batter came out like the original.

Step 4 of 5

Aim for the milk

The ring on the bottom line marks 750 ml, all the milk left in the carton. Move Marker until the milk reaches the ring, then press Check. $750$⁠ sits between two ticks, so the flour will not be a whole number of recipes either.

Step 5 of 5

The amount for one

A way that works for any amount: first find how much milk goes with one gram of flour, the amount for one, then multiply by the flour. Two equal ratios, such as $200 : 300$⁠ and $350 : x$⁠, are called a proportion, and you can also write them as two equal fractions.

Marker is locked at 350 g, which is not a whole number of recipes. Answer, then drag Look inside and compare with the bottom line on the board.