Multiple choice

Pipe 'A' can fill a tank in 18 hours and pipe 'B' can fill in 30 hours. Both the pipes opend together but after 5 hours pipe 'B' closed. In how many hours will pipe 'A' take to fill the remaining part of tank. पाइप A किसी टंकी को 18 घंटे में तथा पाइप B उसी टंकी को 30 घंटे में भर सकते है। दोनों पाइप साथ में खोले जाते है। लेकिन 5 घंटे बाद पाइप B को बन्द कर दिया जाता है। बचे हुए भाग को पाइप A कितनी देर में भरेगा?

  1. 15 hr./घं.

  2. 18 hr./घं.

  3. 10 hr./घं.

  4. 12 hr./घं.
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Pipe A fills at rate 1/18 per hour. Pipe B fills at rate 1/30 per hour. Combined rate = 1/18 + 1/30 = 5/90 + 3/90 = 8/90 = 4/45 per hour. In 5 hours together, they fill 5×4/45 = 20/45 = 4/9 of the tank. Remaining part = 1 - 4/9 = 5/9. Pipe A alone fills at 1/18 per hour, so time for remaining part = (5/9)/(1/18) = 5/9 × 18 = 10 hours.

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