A is thrice as efficient as B and is, therefore, able to finish a piece of work 10 days earlier than B. In how many days A and B will finish it together?

One Answer on this Question

1. Let n be the number of days it takes A and B, working together, to finish. And we know B=A+10 and B=3A, so:

   3A=A+10

   2A=10

   A=5

   Then B=15

   So:

   1/A + 1/B=1/n where n is the total amount of days. So:

   1/5 + 1/15=1/n

   3n+n=15

   n=15/4 days

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