One tap can fill a cistern in 3 hours and the waste pipe can empty the full cistern in 5 hours. In what time will the empty cistern be full, if the tap and the waste pipe are kept open together?

The value of a when

is:

1. 1

2. 1.5

3. 9

4. 6

15 note books can be bought for ₹ 240. The number of note books that can be bought for ₹ 160 is:

1. 16

2. 10

3. 18

4. 15

6 men can do a certain piece of work in 15 days. The number of men required to complete the same work in 10 days:

1. 30

2. 25

3. 60

4. 9