Multiple choice

A reservoir can be filled by 4 pipes in 30, 40, 60 and 120 hours, respectively. The first was opened at 6 am, second was opened at 7 am, third was opened at 8 am and fourth was opened at 9 am. At what time will the reservoir be completely full?

  1. 4 pm

  2. 7 pm

  3. 5 pm

  4. 1:30 pm

  5. 7 am
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Let the time taken after 6 am be t hours.
Therefore, (t/30) + ((t - 1)/40) + ((t - 2)/60) + ((t - 3)/120) = 1                  4t + 3(t - 1) + 2(t - 2) + t - 3 = 120                                           t = 13 hours Therefore, the reservoir will be filled at 7 pm.  It is the correct answer.

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