Question

a car moves 20 km at a speed of 40 km per hour and the next 10 m in 3 minutes calculate its average speed

Answer 1

first we have to convert the values 
.1000/10=100
.60/3=20

average speed =total distance travelled /total time taken
 dist=100+20=120
time=20+40=60
                         =120/60
                         =2 km/hr
hopefully helpful...

Answer 2

in first case , T=D/s
20 km  / 40 km/h =1/2 hr or 0.5 hr
in second case,D=10m,T=3min
20 km=2000m,0.5hr=30 min
D= 2000+10=