Multiple choice

Two pipes A and B can fill a cistern in 24 minutes and 32 minutes respectively. If both the pipes are opened together, then after how many minutes B should be closed so that the cistern is full in 18 minutes? दो पाइप A और B एक हौज को क्रमशः 24 मिनट और 32 मिनट में भर देते है। यदि दोनों पाइप एक साथ खोल दिये जाये तो कितने मिनट बाद B को बंद कर दे कि हौज 18 मिनट में भर जाये?

  1. 6

  2. 8

  3. 10

  4. 12

Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Pipe A fills at 1/24 per minute, Pipe B at 1/32 per minute. Let B be closed after x minutes. Both work for x minutes: x(1/24+1/32) = x(7/96). Then A works alone for 18-x minutes: (18-x)(1/24). Total = x(7/96)+(18-x)(1/24) = 7x/96+18/24-x/24 = 7x/96+3/4-4x/96 = 3x/96+3/4 = 1. Solving: 3x/96 = 1/4, x = 8. So B should be closed after 8 minutes.