alleryA can do a piece of work in 10 days and B in 15 days. Working together they finish it in:
A5 days
B7.5 days
C6 days
D12.5 days
Answer & Solution
Correct answer: C. 6 days
1. Work with the fraction each finishes in one day.
2. A does one tenth of the work per day and B does one fifteenth.
3. Together they do 1/10 + 1/15 = 3/30 + 2/30 = 5/30, which is one sixth per day.
4. Completing the whole job therefore takes 6 days.
5. Averaging 10 and 15 to get 12.5 is the classic error; two people together must be faster than either alone.
_Source: syllabus Maths, Ch 11 'Direct and Inverse Proportions', S11.3 Inverse Proportion_
Keep practising Time and Work
Browse all Time and Work questions for AFCAT, or explore more Quantitative Aptitude topics.
Related questions
For a fixed amount of work, the product of the number of workers and the days taken is:A can finish a job in 20 days. After working 5 days he leaves. The fraction of work left iA pipe fills a tank in 6 hours while an outlet empties it in 8 hours. With both open the tA is twice as fast as B. Working together they finish a job in 8 days. A alone would take:A and B together finish a job in 12 days. A alone takes 20 days. B alone would take:If 12 workers can complete a task in 8 days, 16 workers will complete it in:If 6 men finish a job in 10 days, how many days will 4 men take at the same rate?As the number of workers on a job increases, the time taken to finish it: