Tuesday

October 21, 2014

October 21, 2014

Posted by **Anonymous** on Tuesday, January 8, 2013 at 10:32am.

- maths -
**Jennifer**, Wednesday, January 9, 2013 at 7:37pmLet the rate at which A works be a; the rate at which B works be b; the rate at which C work be c:

(a + b)*12 = 1

(b + c)*15 = 1

a = 2*c

gives

b + a/2 = 1/15

b = 1/15 - a/2

Substituting into the first equation:

(a + 1/15 - a/2)*12 = 1

a/2 + 1/15 = 1/12

a/2 = 1/12 - 1/15 = (15-12)/(15*12)

a/2 = 3/(15*12) = 1/(5*12) = 1/60

a = 1/30

The rate at which a works is 1/30 of the work per day; so a will complete the task in 30 days.

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