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Pipes A (6 hours) and B (4 hours) are opened alternately for 1 hour each, A first. How long does the tank take to fill?

Competition practiceTime & Work / Pipes

A5 hours
B4 4/5 hours
C5 1/3 hours
D6 hours

Step-by-Step Solution

Pair:

\frac{2 + 3}{12} = \frac{5}{12}

. After 4 h:

\frac{10}{12}

. Hour 5 (A) adds

\frac{2}{12}

: full at exactly 5 hours.

Answer: A) 5 hours

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