Travelling at 80 kmph a person can reach his destination in a certain time. He covers 3 /4 of the journey in 4/ 5 of the total time. At what speed should he travel the remaining distance to reach his destination on time?
Answers
Answer:
100 km/h
Step-by-step explanation:
We can solve this in two ways, I will show you both ways, so here we go.........
Method 1
Let the Total Distance for the Journey be 'D' km and Total Time be 'T' hrs
Thus,
D/T = 80 km/h ---- 1
Now,
According to the Question,
He travelled 3/4 of the distance in 4/5 of time
That is, (3/4)D in (4/5)T
Now, distance left = D - (3/4)D
= (4/4)D - (3/4)D = (1/4)D
and time left = T - (4/5)T
= (5/5)T - (4/5)T = (1/5)T
Thus, we need to find the speed required to travel (1/4)D in (1/5)T
Speed = Distance/Time
= (1/4)D ÷ (1/5)T
= D/4 × 5/T
= 5/4(D/T)
From eq.1 we get D/T = 80 km/h
Speed = (5/4) × (80)
Speed = 100 km/h
Thus, he must travel with a speed of 100 km/h to reach his destination on time.
Method 2
We know that,
Total Distance covered ÷ Total time taken = 80km/h
Let the certain time mentioned here be 'x' hrs
Speed = Distance/Time
then,
Distance = Speed × Time
Distance = 80 × x = 80x km
Now,
He covers 3/4 of the distance in 4/5 of the time
so, Distance covered = 80x × (3/4) = 60x km
and the time taken = x × (4/5) = (4/5)x
Now the distance left = 80x - 60x = 20x km
So, he has 20x km more to finish his journey
Time left = x - (4/5)x = (5/5)x - (4/5)x = (1/5)x
So, he has (1/5)x more to finish his journey
Now,
He has to complete 20x km in (1/5)x hrs
then,
Speed = 20x/(1/5)x = 20x ÷ (1/5)x
= 20x × (5/x) = 20 × 5 = 100 km/h
Thus, he must move with a speed of 100 km/h to reach the destination on time.
Hope it helped and you understood it........All the best