4. A, B and C working together can do a piece of work in 8 hours. A alone can do it in 20 hours and B alone can do it in 24 hours. In how many hours will C alone do the same work?
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Step-by-step explanation:
A,B,C working together complete a work in 8 hours.
∴ In one hour they can complete
8
1
th of work.
A can alone do the work in 20hr
∴ In one hour A can complete
20
1
th of work.
B can alone do the work in 24hr.
∴ In one hour B can do
24
1
th of work.
Let in one hour C can do
x
1
th of work.
∴
20
1
+
24
!
+
x
1
=
8
1
⇒
x
1
=
8
1
−(
20
1
+
24
1
)
=
8
1
−
20×24
44
=
8
1
−
120
11
=
120
15−11
=
120
4
=
30
1
∴ C can do the same work in 30 hours.
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