Answer:
Julia rode 4.17 miles per hour faster than Katie.
Explanation:
Julia can finish a 20 mile bike ride in 1.2 hours.
Katie can finish the same bike ride in 1.6 hours.
Julia finished the bike ride faster than Katie, so we have to calculate how much Julia is faster.
Now we have to calculate the difference of the speed of both.
Speed =

Julia's speed =
= 16.67 miles/hour
Katie's speed =
= 12.5 miles/hour
The difference between the speed = 16.67 - 12.5 = 4.17 miles/hour
Therefore, Julia rode 4.17 miles per hour faster than Katie.