It takes 37 minutes and 45 minutes for two pipelines A and B to fill a cistern, respectively. Both of the pipes have been opened. If the B is switched off after: the cistern will be filled in less than half an hour.
A. 5min.
B. 9min.
C. 10min.
D. 15min.
Answer:B
It takes 37 minutes and 45 minutes for two pipelines A and B to fill a cistern, respectively. Both of the pipes have been opened. If the B is switched off after: the cistern will be filled in less than half an hour.
A. 5min. B. 9min. C. 10min. D. 15min.
Explanation: Allow x minutes for B to be switched off. ThePart filled in x minutes by (A + B) + Part filled in (30 -x) minutes by A = 1.× 2/75 + 1/45 + (30 - x).1 = 2/75,1 = 11x/225 + (60 -2x)/75.225 = 11x + 180 - 6x.x equals 9.