Two pipes can fill a tank in 20 hours and 90 hours, respectively. The time (in hours)
required to fill the tank when both pipes are opened simultaneously is:
-
A.
179/9
-
B.
183/8
-
C.
177/13
-
D.
180/11
Correct Answer:
D. 180/11
Explanation:
The correct answer is Option D: 180/11.
To find the time taken when both pipes work together, we calculate their combined hourly rate. The first pipe fills 1/20 of the tank per hour, and the second pipe fills 1/90 of the tank per hour. Adding these rates gives (1/20 + 1/90), which simplifies to (9 + 2) / 180, or 11/180 of the tank per hour. To find the total time required to fill the entire tank, we take the reciprocal of this combined rate, resulting in 180/11 hours.
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