Question

A car is moving at a constant speed covers a distance of 180 km in 3 hours. Find the time taken by the car to cover a distance of 420 km at the same speed.

Answer 1

Distance covered = 180 km 

Time taken = 3 Hrs. 

Distance to be covered = 420 km 

Time required = ? = x (say) 

Since the car is moving at a constant speed, we have 

180 : 3 is as to 420 : x 

180 : 3 :: 420 : x 

Its a proportion. 

So, product of extremes = Product of means 

180 × x = 3 × 420

∴ Time required = 7 Hrs. 

(OR) 

Distance covered by a car in 3 hours = 180 km 

Distance covered by a car in 1 hour = 180 ÷ 3 

Time taken to cover 60 km distance = 180/3 = 60 km 

Time taken to cover 420 km distance = 420 ÷ 60 = 420/60 = 7 hours

Answer 2

Speed = Distance (in metres) / time taken (in sec.)

Distance covered = 180km = 180 x 1000 = 180000m

Time taken = 3 x 60 sec. = 180 seconds

speed = d / t

180000 / 180 = 1000 m/s

So the speed is 1000 m/s

now,

Distance covered = 420km = 420 x 1000m = 420000m

speed = 1000 m/s

time taken = ?

S = D/t

so t = S x D

t = 420000m / 1000 m/s

t = 420 seconds

t = 7 hr