A can polish the floors of a hall in 20 days and B can do it in 30 days. With the help of C, they complete the work in 6 days. How long would C alone take to do the job?
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → 12 days
People working together add their one-day work. So C's one-day work is the one-day work of all three minus that of A and B.
One-day work of A, B and C together \(\displaystyle =\frac{1}{6}\)
One-day work of A and B \(\displaystyle =\frac{1}{20}+\frac{1}{30}=\frac{3+2}{60}=\frac{1}{12}\)
One-day work of C \(\displaystyle =\frac{1}{6}-\frac{1}{12}=\frac{2-1}{12}=\frac{1}{12}\)
C alone would take 12 days.