In 1 min,
Tap A fills 1/6,
Tap B fills 1/9 and
Tap C fills 1/5.

LCM of 6, 9 and 5 is 90

For 2 min,
Taps A and C fill [(1/6) + (1/5)] x 2 = 22/30 = 66/90

1 – 66/90 = 24/90 (remaining tank left to fill)
Taps A and B fill (1/6) + (1/9) = 5/18 = 25/90 in 1 min
1/90 ——- 1/25 min
24/90 ——- 24/25 min

Ans : 24/25 min.

Suggested answer:

In 1 minute time,

A filled 1/6 of tank –> 15/90 of tank

B filled 1/9 of tank –> 10/90 of tank

C filled 1/5 of tank  –> 18/90 of tank

A and C filled 33/90 of tank (15/90 + 18/90)

A and B filled 25/90 of tank (15/90 + 10/90)

In 2 min, A and C filled 66/90 of tank (33/90 x 2).

Therefore remaining of tank to be filled will be 24/90 of tank (1 – 66/90).

In 1 min, A and B filled 25/90 of tank, in order to fill 24/90 of tank, time required will be 24/25 min.