Problems on Calculating Time

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

Speed of Train

Relationship between Speed, Distance and Time

Conversion of Units of Speed

Problems on Calculating Speed

Problems on Calculating Distance

Problems on Calculating Time

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

Train Passes through a Pole

Train Passes through a Bridge

Two Trains Passes in the Same Direction

Two Trains Passes in the Opposite Direction





8th Grade Math Practice

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