circles spining together

[jhjs...@hotmail.com]

I have a question.

Two circles(r1, r2) of radius 10, and 25 are touching
each other and spins without slippage.

when r1 is spining at 50 rpm, at what rpm is r2 spining?
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I think the answer is 20 rpm but I don't know how to
explain logically. Please help.

thanks in advance,

[K12math.com Support]

Answer posted on K12math.com
here

http://www.k12math.com/math-concepts/geometry/rotating-circles-explanation.htm