Discussion

A can do a piece of work in 12 days and B in 18 days. Working together, in how many days will they finish it ?

Answer: C

Correct answer: 7.2 days

Add the daily rates rather than the times.

\[\frac{1}{12} + \frac{1}{18} = \frac{3}{36} + \frac{2}{36} = \frac{5}{36}\]

Working at five thirty-sixths of the job per day, they need

\[\frac{36}{5} = 7.2 \text{ days}\]

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