A store sells yogurt only in servings of 6 ounces and 9 ounces. If the store sold 75 servings of yogurt for a total of 600 ounces of yogurt, how many 9-ounce servings did they sell?

50

Explanation:

Let the amount of 6 ounces servings be 'x'

and the amount of 9 ounces servings be 'y'

Thus,

According to the question

x + y = 75 servings

or

x = 75 - y ... (i)

and

6x + 9y = 600 ounces ... (ii)

substituting value of x in equation (ii)

6 (75 - y) + 9y = 600

or

450 - 6y + 9y = 600

or

3y = 600 - 450

or

y = 150 : 3

or

y = 50