Question

The radius of a circular track is 0.2 mile. Ellie ran around 3 times. How many kilometers did she run

Answer 1

Circumference = 2πr
So the circumference of the track is C = 2π .2  or .4π
3 times around the track is .4π x 3 or 1.2π  - this is the answer but most teachers will want you to use 3.14 for pi.
so 1.2 x 3.14 = 3.768 km

Do you notice that I waited until the end to use the actual value of pi (3.14) in my calculations.
Keeping things in pi units until the very end saves time.