Question

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

• A. 6 days
• B. 7.2 days
• C. 8 days
• D. 9 days

Hint:

Add the per-day fractions, then take the reciprocal.

Answer 1

The Correct Option is B

Step 1: Write one-day work rates.
A does \(\dfrac{1}{12}\) per day, B does \(\dfrac{1}{18}\) per day.
Step 2: Add the rates.
\[\dfrac{1}{12} + \dfrac{1}{18} = \dfrac{3 + 2}{36} = \dfrac{5}{36}\] Step 3: Invert for the time.
\[\text{Time} = \dfrac{36}{5} = \boxed{7.2 \text{ days}}\]