For the past n days, the average (arithmetic mean) daily production at a company was 50 units. If today's production of 60 units raises the average to 55 units per day, what is the value of n ? Choose the correct answer: A) 30 B) 18 C) 10 D) 9 E) 1
(average production for n days) * n = (total production for n days) --&gt; 50n=(total production for n days);   (total production for n days) + 60 = (average production for n+1 days) * (n+1) --&gt; 50n + 60 = 55 * (n+1) --&gt; n=1.   Answer: 1.
<result>E</result>
For the past n days, the average (arithmetic mean) daily production at a company was 50 units. If today's production of 60 units raises the average to 55 units per day, what is the value of n ?