the radius around the circle?

Question

an object travels around a circle with a constant speed. Two measurements are taken: it rotates 21 revolutions in 7 seconds. It travels 40 meters in 5 seconds. find the radius of the circle

Answer 1

21 revolutions in 7 seconds means 3 revolutions in each second

In 5 seconds it's gone 15 revolutions

15 revolutions = 40 meters traveled or 40/15 = 8/3 = 2 2/3 meters per revolution

circumference of the circle is 2pir 8/3 = 2pir r= 8/6pi meters

8/6pi = 4/3pi = 4 divided by 3 times 3.14159 = maybe about .4 meters rounded to one decimal point