Question

A and b can do a piece of work in 20 days b and c im 40 days c and a in 40 days

Answer 1

GIVEN;
A+B=20 ---(1)
B+C=40---(2)
C+A=40---(3)

SOLUTION;
A=20-B---(4)
substitute in (3)..
C+(20-B)=40
C+20-B=40
C-B=40-20
C-B=20
C=20+B---(5)

Substitute C=20+B in (2)..,
B+20+B=40
2B=40-20A=20-10
2B=20
B=10

Substitute B=10 in (4)..
A=20-10
A=10

Substitute B=10 in (5)
C=20+10
C=30

Therefore ,
A do a piece of work in 10 days

B do a piece of work in 10 days

C do a piece of work in 30 days