gmat prep question

[jamesk486]

The normal production rate for a certain machine that runs continuously was n units per day. Over a period of 10 days, the machine was shut down part of the time for cleaning and servicing, but produced at the normal rate when in operation. If the machine's total production during this period was 60% of its normal production, then the total time that the machine was shut down was equivalent to how many days?

(A) 0
(B) 1
(C) 2
(D)4
(E) 6

[jayhawk2001]

The normal production rate for a certain machine that runs continuously was n units per day. Over a period of 10 days, the machine was shut down part of the time for cleaning and servicing, but produced at the normal rate when in operation. If the machine's total production during this period was 60% of its normal production, then the total time that the machine was shut down was equivalent to how many days?

(A) 0
(B) 1
(C) 2
(D)4
(E) 6

Total prod in 10 days working at regular rate = 10*n
60% of above = 6n
num days worked = 6n/10n*10 days = 6 days.
So shutdown for 4 days.

Alternatively, (1-0.6)*10 days = 4 days

[Cybermusings]

Normal production = n units a day or 10n units in 10 days….new production = .6n or 6n in 10 days….or 4n was the loss of production……n units were produced in 1 day….hence 4n units were produced in 4 days….hence (D)