Multiple choice

A tank is filled in $5$ hours by three pipes A, B and C. The pipe C is twice as fast as B and B is twice as fast as A. How much time will pipe A lone take to fill the tank?

  1. $20$ hours
  2. $25$ hours
  3. $35$ hours

  4. Cannot be determined

  5. None of these
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Let pipe A's rate be x. Then B works at 2x and C at 4x, so the combined rate is 7x. Since the tank fills in 5 hours, 7x = 1/5, giving x = 1/35. Pipe A alone therefore takes 35 hours.

AI explanation

Let the time taken by pipe A be x hours, so B takes x/2 hours and C takes x/4 hours. Using the combined work formula, 1 divided by x plus 2 divided by x plus 4 divided by x equals 1 divided by 5. This gives 7 divided by x equals 1 divided by 5, meaning x equals 35 hours.

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