Final answer:
To find the number of cups of water to add to 90 grams of powder at a 1:5 ratio, use the proportion 1 cup/5 cups = x cups/90 grams. Cross-multiply and solve for x. x = 18 cups.
Step-by-step explanation:
To find the number of cups of water to add to 90 grams of powder at a 1:5 ratio, you need to set up a proportion. Since the ratio is 1:5, this means that for every 1 cup of water, there are 5 cups of powder.
To find the number of cups of water, you can set up the proportion 1 cup/5 cups = x cups/90 grams. Cross-multiplying, you get 5x = 1 * 90.
Divide both sides by 5 to find the value of x, which is the number of cups of water.
So x = 90/5 = 18 cups. Therefore, you need to add 18 cups of water to 90 grams of powder.