Question

A and B can do a piece of work in 10 days,B amd C in 15days and C and A 20days .C alone can do the work in.

Answer 1

A+B=1/10 for 1 day
B+C=1/15 for 1 day
C+A=1/20 for 1 day
A+B+B+C+C+A=(1/10+1/15+1/20)
2(A+B+C)=13/60
A+B+C=13/120 for 1 day ----eq(1)
A+B=1/10-----eq(2)
Subtract eq(1)-eq(2)
A+B+C-(A+B)=13/120-1/10
C=1/120
c alone can do the work in 120 days
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