Time & Distance

Distance = Speed × Time.

Using this formula, all basic problems can be handled. However, you need to make sure about the correct usage of units while using the above formulas.

Speed is inversely proportional to the time taken when distance travelled is constant. So when speed increases, time decreases and vice versa.

Average Speed 

Average speed = Total Distance covered / Total Time Taken

When the distance is constant:

         Average speed = 2xy / x+y;

         Where, x and y are the two speeds at which the same distance has been covered.

When time taken is constant:

         Average speed = (x + y) / 2;

         Where, x and y are the two speeds at which we traveled for the same time

Relative Speed

If two bus/train/person moving in same direction with a speed of s1 and s2 respectively.

           Then  the Relative speed will be = s1 – s2

If two bus/train/person moving in opposite direction with a speed of s1 and s2 respectively.

           Then  the Relative speed will be = s1  + s2

A man rides a bike at a speed of 48 km/hr. Find the distance covered by him in 4 hours 15 minutes.

a) 234 km                     b) 214 km                     c) 204 km                     d) 224 km

Solution:

Distance (D) = Speed (S) × Time (T)

Given that, S = 48 km/hr and T = 4 hours 15 minutes = 4 15/60 hours = (17 / 4) hours

⸫ Required distance covered = 48 × (17 / 4) = 204 km.

Answer: c

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