A cake recipe calls for 30 milliliters of water for every 20 milliliters of cooking oil. How many milliliters of water are needed if 50 milliliters of cooking oil were used?

To solve this problem we can set up a proportion, letting x represent the unknown amount of cooking oil.

30 milliliters water/20 milliliters cooking oil = x milliliters water / 50 milliliters cooking oil

30/20 = x/50

To solve this proportion, we can use cross products, also called the means extremes products theorem. This takes the products of the numerator and denominator from the separate fractions and sets them equal to one another. In this circumstance, it results in the equation:

(30) (50) = (x) (20)

When we multiply we get:

1500 = 20x

Finally, we have to divide both sides of the equation by 20 to get our variable x alone on the right side of the equation.

x = 75 milliliters

Therefore, the proportion is completed, as 30/20 = 75/50.

Answer: You need 75 milliliters of water.

50 is 30 more than 20 so that's 20*2+10

So 30*2+15=75

The answer is 75