Page 147 - Maths Skills - 8
P. 147
Direct and Inverse Proportions 145
Let’s Attempt
Example 1: Convert
(i) 36 km/h into m/s (ii) 35 m/s into km/h
5 18
Solution: (i) 1 km/h = 18 m/s (ii) 1 m/s = 5 km/h
5 18
\ 36 km/h = 36 × m/s = 10 m/s. \ 35 m/s = 35 × km/h = 126 km/h.
18 5
Example 2: A person covers a certain distance in 3 hours 15 minutes with a speed of 8 km/h. If he covers the
same distance on bicycle at the rate of 13 km/h, find the time taken by him.
13
Solution: Time taken = 3 hours 15 min = hours, Speed of walking = 8 km/h
4
13
\ Distance = (Speed × Time) = 8 × 4 km = 26 km.
Now, the speed of the bicycle = 13 km/h
Distance 26 km
\ Time taken = = = 2 hours
Speed 13 km/h
Hence, on bicycle the person can cover the same distance in 2 hours.
Example 3: If a car covers a distance of 10.8 km in 6 hours, find the distance covered by the car in 10 hours.
Distance 10.8 km
Solution: Speed = = = 1.8 km/h
Time 6 hours
Hence, the distance covered in 10 hours = (speed × time) = (1.8 km/h × 10 h) = 18 km.
Example 4: A motor covers a distance of 252 km in 7 hours. Find the speed of the motor and convert it into m/s.
Solution: Distance = 252 km Time = 7 hours
Distance 252 km
Speed = = = 36 km/h
Time 7 hours
5
1 km/h = m/s
18
5
\ 36 km/h = 36 × m/s = 10 m/s.
18
Example 5: Hrithik goes to school at the rate of 4 km/h and reaches 9 minutes late. If he goes by a rickshaw at
the speed of 5 km/h, he reaches 6 minutes early. What is his distance to school?
Solution: Let the distance to the school be x km.
Time taken to cover x km at a rate of 4 km/h
Distance x km x x
= = = hour(s) = × 60 minutes = 15x minutes
Speed 4 km/h 4 4
Distance x km
Time taken to cover x km at a rate of 5 km/h = Speed = 5 km/h
x x
= 5 hours = × 60 minutes = 12x minutes
5