Area Problem 3

Geometry Level 4

In the diagram,

  • the centers of the two circles are at the midpoints of adjacent sides of a regular pentagon;
  • the two circles intersect at the center of the pentagon;
  • the area of the pentagon is 900.

What is the total area of the red regions?


The answer is 540.

This section requires Javascript.
You are seeing this because something didn't load right. We suggest you, (a) try refreshing the page, (b) enabling javascript if it is disabled on your browser and, finally, (c) loading the non-javascript version of this page . We're sorry about the hassle.

2 solutions

We note that two halves of the red region at the top vertex of the pentagon fit into the bottom of the circle regions of the left and right vertices.

Therefore the area of the red region is 3 5 \frac 35 the area of the pentagon or A r e d = 3 5 A p e n t a g o n = 3 5 × 900 = 540 A_{\color{#D61F06}red} = \frac 35 A_{pentagon} = \frac 35 \times 900 = \boxed{540} .

elegant solution

albert yiyi - 2 years, 10 months ago

Log in to reply

Glad that you like it.

Chew-Seong Cheong - 2 years, 10 months ago

did the same way.

Niranjan Khanderia - 2 years, 9 months ago
Albert Yiyi
Aug 6, 2018

hint:

Elegant solution. Voted up.

Niranjan Khanderia - 2 years, 9 months ago

Hey Albert, superb problem! Can I make a video on this problem?

Mahdi Raza - 9 months, 1 week ago

0 pending reports

×

Problem Loading...

Note Loading...

Set Loading...