Page 144 - Maths Skills - 8

142 Maths

1
Second inlet tap’s 1 hour’s work =
15
Outlet tap’s 1 hour’s work = 1
8
If all three taps are turned on together, then in 1 hour the work done


= 1 + 1 + − 1  = 1 + 1 − 1 = 12 815+− = 20 15- = 5 = 1

10 15  8 10 15 8 120 120 120 24
Thus, the empty tank will be filled up in 24 hours, if all the three taps are turned on together.

Exercise 9.4

1. Two inlet pipes A and B can fill an empty cistern in 2 hours and 4 hours, respectively. If both are opened
together in the empty cistern, how much time will they take to fill it completely?

2. Tap A can fill an empty cistern in 2 hours while the outlet pipe B can empty it in 3 hours. How long will
it take to fill the cistern if both the tap and the pipe are opened simultaneously?
3. A tap can fill up an empty tank in 8 hours. Another tap can empty it in 10 hours. How long will it take
to fill up the empty tank if both the inlet and the outlet taps are turned on together?

4. Three taps A, B and C can fill an empty water tank in 6 hours, 8 hours and 12 hours, respectively. How
long would the three taps take to fill the empty water tank if all of them are opened simultaneously?

5. Taps X and Y can fill up an empty tank in 15 and 12 hours respectively. Another tap Z can empty the
full tank in 8 hours. If all the taps are turned on together at the same time, in how many hours will the
tank be half full?
6. A tap can fill up an empty tank in 7 hours and another in 5 hours. If both the taps are turned on at the
same, time, how long will it take to fill it up completely?

TIME AND DISTANCE
Suppose a car covers a distance of 60 km in 1 hour. And since, speed is defined as the distance covered by a
moving object in a unit interval of time, we can say that the speed, of the moving car is 60 km per hour, written
as 60 km/h. Here, the word speed means average speed or uniform speed.

Formulae
Relation between Speed, Time and Distance
Distance Distance
(i) Distance = Speed × Time (ii) Time = (iii) Speed =
Speed Time

1. To Convert m/s into km/h 2. To Convert km/h into m/s

1 1km 1000m 5
km 1km/h = = = m/s
1m/s = 1m = 1000 = 3600km = 18km 1hour 3600s 18
1s 1 1000h 5h
m 5
3600 Thus, 1km/h = m/s
18
18
Thus,1m/s= km/hh
5