At a certain restaurant, the average (arithmetic mean) number of customers served for the past x days was 85. If the restaurant serves 120 customers today, raising the average to 90 customers per day, what is the value of x? Choose the correct choice from the following answers
A) 2  B) 5  C) 6  D) 15  E) 30
WITHOUTusing the formula, we can see that today the restaurant served 30 customers above the average. The total amount ABOVE the average must equal total amount BELOW the average. This additional 30 customers must offset the “deficit” below the average of 90 created on the x days the restaurant served only 85 customers per day.   30/5= 
<gadget id="calculator">30/5</gadget>
<output>6</output>
6 days.Choice (A).   WITHthe formula, we can set up the following:   90= (85x + 120)/(x + 1)   90x + 90 = 85x + 120   5x = 30   x = 6Answer 6hoice (6)
<result>C</result>
At a certain restaurant, the average (arithmetic mean) number of customers served for the past x days was 85. If the restaurant serves 120 customers today, raising the average to 90 customers per day, what is the value of x?