Question

The distance covered in 5 laps of a circular track is 400pi metres.
What is the shortest distance between any point on the track and the centre?

Answer 1

circumference of track = 400pi / 5 = 80 pi
the shortest distance to centre = radius of circle so
pi r^2 = 80 pi
r^2 = 80
r = sqrt80

Answer 2

a) 400 m
b) 200 m
c) 80 m
d) 40 m

My teacher said its not 80 m.

Answer 3

oh sorry - i used the area of circle (pi r^2) instead of the circumference - silly me
its 2 pi r = 80 pi
so
2r = 80
r = 40 m

d)

Answer 4

Alright, thank you!

Answer 5

80 came form dividing 400 to 5 right?

Answer 6

@cwrw238 did you divide 80 by 2 to get 40 and divide 400 by 5 to get 80?

Answer 7

i divided 400pi by 5 to get 80 pi
and 80 m by 2 to get 40 m