At a certain restaurant, the average (arithmetic mean) number of customers served for the past x ...
At a certain restaurant, the average (arithmetic mean) number of customers served for the past x days was 75. If the restaurant serves 120 customers today, raising the average to 80 customers per day, what is the value of x?
Answer/Solution
8
Steps/Work
WITHOUTusing the formula, we can see that today the restaurant served 40 customers above the average. The total amount ABOVE the average must equal total amount BELOW the average. This additional 40 customers must offset the “deficit” below the average of 80 created on the x days the restaurant served only 75 customers per day.
40/5 = 8 days.Choice (A).
WITHthe formula, we can set up the following:
80 = (75x + 120)/(x + 1)
80x + 80 = 75x + 120
5x = 40
x = 8Answer Choice (D)
40/5 = 8 days.Choice (A).
WITHthe formula, we can set up the following:
80 = (75x + 120)/(x + 1)
80x + 80 = 75x + 120
5x = 40
x = 8Answer Choice (D)