SSC Multi Tasking Model Paper 7

(d) Part of the cistern filled in 1 hour
when pipes P and S are open
=

1

4

−

1

10

=

5−2

20

=

3

20

Hence, the cistern w ill be filled in

20

3

hours ≈6.6 hours
Part of the cistern filled in 1 hour
when pipes P, R and S are open
=

1

4

+

1

12

−

1

10

=

15+5−6

60

=

14

60

=

7

30

Hence, the cistern w ill be filled in

30

7

hours ≈4.3 hours
Part of the cistern filled in 1 hour
when pipes P, g and S are open
=

1

4

+

1

8

−

1

10

=

10+5−4

40

=

11

40

Hence, the cistern will be filled in40—hours ≈ 3.6 hours