Digital PSAT Math Practice Question 173: Answer and Explanation

Question: 173

Eloise is told by her doctor that she should try to average 9 hours of sleep a night, since that is what a typical teenager needs for optimal mental and physical health. If Eloise has been awake for 126 hours in a given week, how many additional hours of sleep should she have had in order to follow her doctor's advice?

Correct Answer: 21

Explanation:

(21) In a typical week, Eloise should get 9 × 7 = 63 hours of sleep. We can see how much sleep she has gotten by subtracting the total hours she has been awake from the total hours in a week: 24 × 7 - 126 = 42. Then, we can calculate the additional hours of sleep she should get by subtracting how many hours she actually got (42) from the amount of sleep she should have gotten (63):

63 - 42 = 21 additional hours she should get.