romitvsingh wrote: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 55 units per day, what is the value of n?
a) 30
b) 18
c) 10
d) 9
e) 7
This is a weighted average problem.
A production rate of 50 is being combined with a production rate of 90 to yield an average production rate of 55.
We can use alligation, which dictates the following:
The proportion needed of each production rate is equal to the distance between the OTHER two production rates.
Proportion needed of the 50/day rate = |55-90| = 35.
Proportion needed of the 90/day rate = |55-50| = 5.
50/day rate : 90/day rate = 35:5 = 7:1.
Since 7 days at 50/day are needed for every 1 day at 90/day, n=7.
The correct answer is
E.
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