Average problem

[phoenix9801]

3-
A production line averaged 40 units for the past d days. Today, this production line produced 100 units, increasing the average by 25%. What is the value of d?

A) 5
B) 9
C) 10
D) 20
E) 30

[Jim@StratusPrep]

The average increases to 50 based on the information. Thus, (40d+100)/d+1 = 50.

40d + 100 = 50d + 50

50 = 10d

D= 5