Answers

2014-09-19T13:16:56+05:30
Work done by 'A' in 15 days = 1 work
so, work done by 'A' in 1 day = 1/15 part of a work
And,
     work done by'B' in 30 days = 1 work
so, ,work done by 'B' in 1 day = 1/30 part of a work
there work done by (A+B) in 1 day = 1/15+1/30 = 1/10 part of a work.
     1/10 part of a work done by (A+B) in 1 day
so, 1 work done by (A+B) in  \frac{1}{ \frac{1}{10} } days = 10 days
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2014-09-19T15:13:06+05:30
A can do a work in= 15 days
B can do a work in= 30 days
A's one day work rate= 1/15
B's one day work rate=1/30
To get their work rates combined, we'll add them=
 1   +      =   2 + 1     =      =   1  
15      30           30            30        10
To get the no. of days we do the reciprocal.
So the ans is 10 days.
:)
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