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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