Multiple choice

Two pipes A and B can fill the tank in 16 hours and 20 hours respectively. If both the pipes are simultaneously opened in an empty tank, what part of the tank is filled after 8 hours?

  1. $3/5$
  2. $9/10$
  3. $3/10$
  4. $9/12$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Pipe A fills 1/16 of the tank per hour, and pipe B fills 1/20 per hour. Together they fill 1/16 + 1/20 = 9/80 per hour. In 8 hours, they fill 8 × (9/80) = 9/10 of the tank. Alternatively: in 8 hours, A fills 8/16 = 1/2 and B fills 8/20 = 2/5, so total = 5/10 + 4/10 = 9/10.

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