Multiple choice

Six taps can fill an empty cistern in $8$ hours. How much more time will be taken, if two taps go out of order? Assume all the taps supply water at the same rate.

  1. $1$ hour
  2. $2$ hours
  3. $3$ hours
  4. $4$ hours
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Work done by 6 taps in 1 hour is 1/8 of the cistern. Work done by 1 tap in 1 hour is 1/48. With 4 taps, work done in 1 hour is 4/48 = 1/12. Time taken = 12 hours. The increase in time is 12 - 8 = 4 hours.

AI explanation

Using the total work formula, the total work needed to fill the cistern is six taps multiplied by eight hours, equalling forty-eight tap-hours. If two taps go out of order, only four taps remain working. Dividing the total work of forty-eight tap-hours by the four working taps gives a new filling time of twelve hours. The increase in time is twelve hours minus the original eight hours, resulting in an extra four hours.