Question:
A, B and C can do a piece of work in 10 days, 12 days and 15 days respectively. How long will they take to finish it if they work together?
Solution:
Time taken by A to complete the work $=10$ days
Time taken by B to complete the work $=12$ days
Time taken by C to complete the work $=15$ days
Work done per day by A $=\frac{1}{10}$
Work done per day by B $=\frac{1}{12}$
Work done per day by C $=\frac{1}{15}$
Total work done per day $=\frac{1}{10}+\frac{1}{12}+\frac{1}{15}=\frac{6+5+4}{60}=\frac{15}{60}=\frac{1}{4}$
A, B and C will take 4 days to complete the work if they work together.