RRB Group-D Model Paper 13 with answers for online practice

GIVEN:
Two pipes can fill a tank in 12 hours and 15 hours respectively.
CONCEPT:
Total work = Time × Efficiency
CALCULATION:
Suppose total capacity of tank = 60 units (LCM of 12 and 15)
So,
Efficiency of pipe 1 = 60/12 = 5 units
Efficiency of pipe 2 = 60/15 = 4 units
So,
Tank filled in 4 hours = (5 + 4) × 4 = 36 units
Remaining tank to be filled = 60 – 36 = 24 units
Hence,
Remaining 24 units of work will be filled by second pipe in 24/4 = 6 hours.