physics

Suzanne bikes 3 km to school every day. It takes her 20 minutes because she always has to stop at a traffic light. What is her average speed?
A. 0.15 km/s
B. 3 m/s
C. 6.7 km/minute
D. 9 km/h

i keep picking A and C and getting this wrong. i know this is the formula:

s = d/t

but when you do it the time conversion isn't correct, and when i try to multiply it by 60 or figure it out it doesn't work. :( how do i do this?

asked by forrest
  1. 0.15 is in minutes, and when i convert it to seconds it's 9, but the only available answer for 9 is 9 km/h, which makes no sense, so is it B?

    posted by forrest
  2. no, it was D... i don't understand how but it was

    posted by forrest
  3. 3 km/20 min = 3 km / (1/3)hr = 9 km/hr

    posted by Damon
  4. The point is that 20 min = 1/3 hour

    posted by Damon

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