A bicycle travels 10km in 20 min.

1.6 km = 1 mile
1 km = 1/1.6 mile
10 km = 1/1.6 x 10= 6.25 miles
60 minutes = 1 hour
1 min = 1/60 hour
20 minutes = 1/60 x 20 hour = 1/3 hour
speed = distance/time= 6.25 miles/1/3 hour = 18.75miles/hour

Question: 10 km / 20 min = ? Mi/hr

Answer:

First, convert 10 km to its equivalent in miles.
Second, convert 20 min to its equivalent in hours.

I'll do the second part for you:
20 min x (1 hr / 60 min) = 1 / 3 hrs = 0.333 hrs

I'll leave it as an exercize for you to determine
the first part (converting 10 km to miles).

Finally, divide the answer for the first part by
the answer for the second part, above.

Average speed = avg. velocity = distance / time = v = d / t.