For the past n days, the average (arithmetic mean) daily production at a company was 50 units. If today's production of 90 units raises the average to 52 units per day, what is the value of n ? Answers
A) 30 B) 19 C) 10 D) 9 E) 7
(average production for n days) * n = (total production for n days) --&gt; 50n=(total production for n days);   (total production for n days) + 90 = (average production for n+1 days) * (n+1) --&gt; 50n + 90 = 52 * (n+1) --&gt; n=19.   Or as 40 extra units increased the average for n+1 days by 2 units per day then 40/(n+1)=2 --&gt; n=19.   Answer:19.
<result>B</result>
For the past n days, the average (arithmetic mean) daily production at a company was 50 units. If today's production of 90 units raises the average to 52 units per day, what is the value of n ?