Circle circle circle

Geometry Level 2

The 2 blue circles are equal in size.

What is the ratio of the blue region to the red region?

1:2

3:5

1:1

2:3

2 solutions

Jason Hughes
Mar 31, 2015

Give inner circle radii of $r$ and outer circle radii of $2r$ . Area of two blue circles is $2\pi r^2$ and area of red area is $4\pi r^2 - 2\pi r^2$ or $2\pi r^2$ . Areas are the same so 1:1 ratio.

ohhh....i compared it with the area of whole circle !!!! idiot me !!

Tootie Frootie - 6 years, 2 months ago

I did the same. I don't think that we are idiot. It is kinda double thinking. I mean, we do imagine that under the blue ones still there the red region. I am OK with that.

Helom Bento - 6 years ago

yaa ..it happens ....sometimes ....

Tootie Frootie - 6 years ago

Arun Sabarish
Apr 13, 2015

Let's take radius of outer circle is 2 and that of inner circle is 1. The ratio becomes, (2×π×1)/(1×π×2^2 - 2π), 2π/2π. = 1 : 1

Circle circle circle

2 solutions

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