For the past n days, the average (arithmetic mean) daily production at a company was 50 units. If today's production of 100 units raises the average to 55 units per day, what is the value of n?
Choose the correct choice from the following.
A) 6
B) 7
C) 8
D) 9
E) 10
The daily production was raised by 5 units for n days, which has a weighting of 5n.   5n = 100-55= 
<gadget id="calculator">100-55</gadget>
<output>45</output>
45   n= 9   The answer is 9.
<result>D</result>
For the past n days, the average (arithmetic mean) daily production at a company was 50 units. If today's production of 100 units raises the average to 55 units per day, what is the value of n?