From Delta math

Question

A pancake recipe calls for 7 eggs and 21 cups of flour. How many cups of flour would you need for a single egg?

Answer 1

the proportion here is

7 egg : 21 flour = 1 egg : 3 flour

meaning that you need 3 cups of flour for a single egg

Answer 2

Since 7 eggs = 21 cups of flour, we can divide both sides of the equation by 7, leaving us with 7 eggs / 7 = 1 egg and 21 cups of flour / 7 = 3 cups of flour.

Answer 3

A method that works even if the numbers are not easily divisible is to set up a proportion (ratios that are equal to each other). I strongly recommend including the units with all the numbers given to you in word problems. For example, not just "21," but "21 cups of flour."

7 eggs ₌ 21 cups of flour _OR 7 eggs ₌ 1 egg

1 egg ? cups of flour 21 cups of flour ? cups of flour

Proportions require that the units above/below each other to be the same

OR

that the units left/right of each other are the same and the units in each ratio refer to *one* pair of terms from the same situation.

These two attempts at writing the proportion for this word problem are incorrect:

7 eggs = 21 cups of flour 7 eggs ₌ ? cups of flour

? cups of flour 1 egg 21 cups of flour 1 egg

To start solving, cross multiply. From either of the two correctly written proportions you will get

(7 eggs)(? cups of flour) = (21 cups of flour)(1 egg)

which can be streamlined a bit and be written 7x = 21.

Remember, x = unknown number of cups of flour.

To get the x alone (very important!) divide both sides by 7:

7x ₌ 21

7 7

which can be simplified to x = 21/7, which can be further simplified to x = 3.

Answer: For one egg you would need three cups of flour.

Answer 4

7 eggs = 21 C flour

1 egg = 3 C flour, divide both sides by 7