A tank can be filled by one tap in 20 minutes and by another tap in 60 minutes. Both taps are kept open for 10 minutes, and then the first tap is shut off. After this, in how much more time will the tank be completely filled?
A
10 mins
B
15 mins
C
20 mins
D
25 mins
Correct Option:
C
Explanation
Together, the taps fill 1/20 + 1/60 = 1/15 of the tank per minute, so in 10 minutes they fill 2/3. After the first tap is shut, the second tap needs 20 more minutes to fill the remaining 1/3.
