Tap A can fill a tank in 12 hours and tap B can

Solution

Let tank capacity is = 60 liter LCM of 12 and 15 So tap A can fill it in 12 hours ∴ Tap A can fill per hours = 60/12 = 5 ltr Tap B can emptied it in 15 hours ∴ Tap B can empty per hours = 60/15 = 4 ltr Tank filled after 2 hour = 5 - 4 = 1 ltr (If taps open alternatively) In last hour tap A fill tank 5 ltr So rest part of tank need to be filled is = 60 - 5 = 55 ltr In 2 hours tank filled = 1 ltr So 55 ltr to be filled in = 55 × 2 = 110 ∴ So total time = 110 + 1 = 111 hours Alternate Method: A B 12 15 LCM = 60 5 : -4 As both taps are working in alternate, So tank filled in 2 min = 5-4 = 1Liter So tank filled in 110 min = 55 Liter & in next minute , 1st tap will fill the remaining 5 Liter in next 1 minute Hence total time = 110 +1 = 111 minute