In 15 minutes and 20 minutes, two pipelines A and B can fill a tank, respectively. Both pipes are opened simultaneously, but pipe A is switched off after 4 minutes. How long will it take to fill the tank completely?
A. 10 min. 20 sec.
B. 11 min. 45 sec.
C. 12 min. 30 seC.
D. 14 min. 40 sec.
Answer:D
In 15 minutes and 20 minutes, two pipelines A and B can fill a tank, respectively. Both pipes are opened simultaneously, but pipe A is switched off after 4 minutes. How long will it take to fill the tank completely?
A. 10 min. 20 sec. B. 11 min. 45 sec. C. 12 min. 30 seC. D. 14 min. 40 sec.
Explanation: Filling the part in 4 minutes = 4 1/15+1/20= 7/15.The remaining portion is equal to 1 - 7/15 = 8/15.B filled 1/20 of the part in 1 minute.1/20 : 8/15 : :1 :x10 2/3 min = 10 min. 40 sec. The tank will be full in 4 minutes, 10 minutes, and 40 seconds, for a total of 14 minutes and 40 seconds.