Question

Question # 2:
A train travels 68km at an average speed of 51km/h. It then travels
another 20 km at an average speed of 40 km/h before reaching its
destination. Calculate the average speed for the whole journey.

Answer 1

Given :-

A train travels 68 km at an average speed of 51 km/h.

It then travels  another 20 km at an average speed of 40 km/h before reaching its  destination.

To Find :-

Calculate the average speed for the whole journey.

Analysis :-

Time = Distance/Speed

Average speed = Total distance/Total time

Solution :-

We know that,

• t = Time
• d = Distance

Finding the time,

$\underline{\boxed{\sf Time=\dfrac{Distance}{Average \ speed} }}$

Substituting their values,

Time = 68/51

= 1 1/3 hour

Given,

Distance = 20 km

Speed = 40 km/h

Time = Distance/Speed

By substituting,

Time = 20 ÷ 40 = 1/2 hour

Total Distance = 68 + 20

= 88 km

Now finding,

Total Time = 1 1/3 + 1/2

= 1 5/6 hours

By the formula,

$\underline{\boxed{\sf Average \ speed=\dfrac{Total \ distance}{Total \ time} }}$

Substituting them,

Speed = 88 ÷ 1 5/6

= 48 km/hr

Therefore, it takes 48 km/hr for the whole journey.