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Comment on The SAT Question Everyone Got Wrong

FrankTheHealer@lemmy.world ⁨1⁩ ⁨year⁩ ago

So I’m confused. I saw this and initially thought it was just a matter of circumference. Suppose the radius of circle A is 10 and the radius of circle B is twice that amount, so it’s 20

The formula to find the circumference of a circle is C = 2πr

So for circle A;

2π10 = 62.831

And for circle B;

2π20 = 125.663

Then to find the difference in circumferences, divide them

125.663/62.831 = 2.000

Therefore, it should take two rotations to rotate one circle around the other

What am I getting wrong here?

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SaakoPaahtaa@lemmy.world ⁨1⁩ ⁨year⁩ ago
You could just watch the vid you know

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CommationCerebrole@jlai.lu ⁨1⁩ ⁨year⁩ ago
There’s one extra-rotation from an external perspective due to the revolution of one around the other. So the formula is r1 / r2 + 1.

This extra-rotation doesn’t appear from the point of view of the circles, or if you consider the circles as two stationary gears

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