### Brain Teasers

# Space Race

If planet A is circling the sun at 5000 miles per hour, and is 30,000 miles from the sun, how fast does planet B have to go to keep up if it is 50,000 miles from the sun?

### Hint

Circumference of a circle = 2*pi*radius### Answer

8333 miles per hour.Because circumference of a circle is first order, 2*pi*r, the ratio can be set up: 5000/30000= X/50000

5000*50000/30000= 5000*5/3= 25/3*1000= 8.333*1000= 8333. No calculator needed!

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