Question

Abus goes to City 1 from City 2 at the speed of 60 km/h. Another bus leaves City 1 for City 2 at the
same time as the first bus, at the speed of 70 km/h. What is the average speed for the journeys of the
two buses combined, if it is known that the distance from City 1 to City 2 is 420 km?​

Answer 1

Answer:

average speed for journey is 65km/h

Explanation:

60+70 = 130

130/2 =65

Answer 2

The average speed for the journeys of the two buses combined is 64.6154 km/h.

Explanation:

To Find: The average speed of the two buses combined

Formula Used:

Average Speed= $\frac{Total distance covered}{Total time taken}$

Speed= $\frac{Distance Travelled}{Time taken}$

Given:

• The speed of the first bus leaving for City 2(v$_{1}$)= 60 km/h
• The speed of the second bus leaving for City 2(v$_{2}$)=70 km/h
• The total distance of their journey from City 1 to City 2= 420 km

We know that the average speed is the total distance covered divided by the total time taken so if we find the total time for the journey of the two buses we can have the answer.

For the first bus leaving for City 2,

Let the time taken by this bus be $t_{1}$

Time =$\frac{distance}{speed}$

∴$t_{1}$= $\frac{420}{60}$h

so, $t_{1}$= 7h

For the second bus leaving for City 2,

Let the time taken by this bus be $t_{2}$,

∴$t_{2}$= $\frac{420}{70} h$

so, $t_{2}= 6h$

Now we have time taken by both the buses which when added becomes the total time for their journey in finding the average speed.

So, average speed= $\frac{Total distance covered}{Total time taken}$

For the two buses combined the total distance becomes 420+420, therefore,

average speed= $\frac{420+420}{t_{1}+t_{2} }$

putting values of time taken for both buses,

average speed= $\frac{840}{7+6}$

adding the denominator part,

average speed = $\frac{840}{13}$

on solving we get,

average speed = 64.6154 km/h

∴The average speed for the two buses combined is 64.6156