Here we will learn to solve different types of problems on calculating time.
We know, the formula to find out time = distance/speed
Word problems on calculating time:
1. A car travel 60 km in 30 minutes. In how much time will it cover 100 km?
Solution:
Using the unitary method;
Time taken to cover 60 km = 90 minutes
Time taken to cover 1 km = 90/60 minutes
Time taken to cover 100 km = 90/60 × 100 = 150 minutes
Formula of speed = distance/time
= 60 km/(3/2) hr [given 1 hour 30 min = 1 30/60 = 1 ½ hours = 3/2 hours]
= 60/1 × 2/3 km/hr = 40 km/hr
Now, using the formula of time = distance/speed = 100 km/40 km/hr = 5/2 hours
= 5/2 × 60 minutes, (Since 1 hour = 60 minutes)
= 150 minutes
2. Victor covers 210 km by car at a speed of 70 km/hr. find the time taken to cover this distance.
Solution:
Using the unitary method;
70 km is covered in 1 hour.
1 km is covered in 1/70 hours.
210 km is covered in 1/70 × 210 hours = 3 hours
Given: speed = 70 km/hr, distance covered = 210 km
Time taken = Distance/ Speed = 210/70 hours = 3 hours
3. A train covers a distance of 36 km in 15 minutes. Find the time taken by it to cover the same distance if its speed is decreased by 9 km/hr.
Solution:
Distance covered by train = 36 km
Time taken = 15 minutes = 15/60 hr = ¼ hr.
Therefore speed of train = Distance covered/time taken
= 36/(1/4) km/hr
= 36/1 × 4/1
= 144 km/hr
Reduced speed = 144 – 9 = 135
Therefore, required time = distance covered/speed
= 36/135 × 60 minutes
= 16 minutes
4. A man is walking at a speed of 6 km per hour. After every km, he takes rest for 2 minutes. How much time will it take to cover a distance of 4 km?
Solution:
Rest time = Number of rests × time of each rest
= 3 × 2 minutes
= 6 minutes
Total time to cover 4 km = 4/6 × 60 + 6 minutes
= (40 + 6) minutes
Relationship between Speed, Distance and Time
Problems on Calculating Distance
Two Objects Move in Same Direction
Two Objects Move in Opposite Direction
Train Passes a Moving Object in the Same Direction
Train Passes a Moving Object in the Opposite Direction
Two Trains Passes in the Same Direction
Two Trains Passes in the Opposite Direction
8th Grade Math Practice
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