‘A’ completes a work in 10 days, while ‘B’ and ‘C’ complete it in 12 a

‘A’ completes a work in 10 days, while ‘B’ and ‘C’ complete it in 12 and 15 days respectively. In how many days can ‘A’, ‘B’ and ‘C’ together complete the work ?

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This question was previously asked in
UPSC CAPF – 2009
‘A’, ‘B’, and ‘C’ together can complete the work in 4 days.
To find the time taken when working together, we calculate the individual daily work rates, sum them up to find the combined daily rate, and then find the reciprocal of the combined rate.
A’s daily work rate = 1/10. B’s daily work rate = 1/12. C’s daily work rate = 1/15.
Combined daily work rate = 1/10 + 1/12 + 1/15.
Finding a common denominator (LCM of 10, 12, 15 is 60):
Combined rate = (6/60) + (5/60) + (4/60) = 15/60 = 1/4.
They complete 1/4 of the work per day.
Time taken to complete the whole work = 1 / (Combined rate) = 1 / (1/4) = 4 days.
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