**Circle Rotation Paradox**

September 1, 2020

**[P6 Maths and beyond: Circles]**

** **

**The following question is a tricky question from 1982 that a lot of people got wrong.**

** **

** **

**It's deceptive (and tempting) to use the large circle B as the point of reference when answering this question. Sure, the circumference of Circle A makes three rounds around Circle B, but that is in relation to the circumference of Circle B as opposed to position of Circle A.**

** **

**In Maths, we must be rigorous with the question and the answer. The question specifies "How many times will Circle A revolve in total", which means the point of reference we must look at is Circle A and how many times it completes a revolution. (in this case, the number of times a point of reference cycles 360 degrees around itself)**

** **

**However many times it may revolve around Circle B does not matter. That simply shows the ratio of A's circumference to B's circumference. It does not solve the question of [# of Circle A revolutions] even though it's intuitive to think so.**

** **

**Be wary of counter-intuitive questions like these. They are especially popular in both PSLE exams, and Express test papers.**

###### Featured Posts

I'm busy working on my blog posts. Watch this space!

###### Recent Posts

###### Archive

###### Search By Tags

I'm busy working on my blog posts. Watch this space!