A car covers the first 80km of its journey at a speed of 40km/h. The driver makes a stop at the tea-stall for 30 minutes and then continues his journey at a speed of 60km/h for 4 hours. What is his average speed (in km/h, correct to 1 decimal place)?

To find the average speed, we use the formula:
Average Speed=
Total Time
Total Distance
​

First part of the journey:

Distance
1
​
=80km

Speed
1
​
=40km/h

Time
1
​
=
40
80
​
=2hours

Stoppage time:

Time
stop
​
=30minutes=
60
30
​
=0.5hours

Second part of the journey:

Speed
2
​
=60km/h

Time
2
​
=4hours

Distance
2
​
=Speed
2
​
×Time
2
​
=60×4=240km

Total Calculation:

Total Distance=80+240=320km

Total Time=2+0.5+4=6.5hours

Average Speed=
6.5
320
​
=
65
3200
​
≈49.23km/h
Rounding to one decimal place, we get 49.2km/h.