I walk 4km at 8km/h and then jog 6km at 12km/h.

Find the total time taken and the average speed for the whole journey.

time walking = 4/8 hrs = 1/2 hr

time jogging = 6/12 hrs = 1/2 hr

total time = 1 hr
avg speed = 10 km/1 hr = 10 km/h