Two Congruent Circles

Geometry Level 2

The above diagram shows 2 congruent circles that are enclosed within a rectangle. Each circle passes through the center of the other circle. Each circle has an area of 10 units.

To the nearest whole number, what is the area of the rectangle?

Details & Assumptions:

1) Area of a circle = Π r 2 =\Pi { r }^{ 2 } .

2) The two circles have the same area.


The answer is 19.

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8 solutions

The area of one of these circles is 3.14 3.14 x r 2 = 10 r^{2} = 10
r 2 = 10 3.14 r^{2} = \frac{10}{3.14}
The area of the rectangle is 2 r 2r x 3 r = 6 r 2 3r = 6r^{2}
= 6 = 6 x 10 3.14 = 19.108 = 19 \frac{10}{3.14} = 19.108 = 19


Sore loser here... I know, okay? The area of the rectangle is 6(r^2) I forgot to round off to the nearest whole number.

Mags Gertos - 6 years, 8 months ago

Simplest is always the best ...

Waleed Mustafa - 6 years, 8 months ago

Details and assumptions are not needed. Everyone should be able to do area of a circle, and it was already specified that both circles have area 10.

Marta Reece - 3 years ago
Trevor Arashiro
Sep 25, 2014

Just a suggestion for further problems like this. It's better if you put, "the area can be expressed as a π \dfrac{a}{\pi} where a is a positive integer. What is the value of a." It just a small change that eliminates the use of a calculator and helps improve your problems. But over all, great problem, quite original.

good ideia

Vasco Estrada Marques Marques - 6 years, 8 months ago
Neha Prabhakar
Oct 3, 2014

area of circle= 22/7r^2=10 r^2=70/22

since the distance between the centers and the center from the border is the radius, the length of rectangle comes out to be 3r.

the breadth is same as the diameter i.e. 2r.

area of rectangle=2r * 3r = 6r^2 = 6* 70/22 =19 (approx.)

Jayraj Inamdar
Sep 27, 2014

The rectangle can be divided into six squares, each having area equal to R^2.

Tejas Sharma
Nov 29, 2014

area of circle =3.14r^2 => 10=3.14r^2 => 10/3.14=r^2 => r=1.78 length of rectangle=3r width of rectangle=2r area of rectangle= 3r * 2r = (5.35*3.569) =19.094= 19

Esha Aslam
Sep 28, 2014

area of circle =3.14r^2 => 10=3.14r^2 => 10/3.14=r^2 => r=1.78

length of rectangle=3r
width of rectangle=2r

area of rectangle= 3r * 2r
= (5.35*3.569) =19.094= 19

Manish Sharma
Sep 27, 2014

r=undr(10/pi);(3r*2r)=19.09859317

bold Good One bold

Md. Nazmus Sakib - 6 years, 8 months ago

Pi.RSquare=10 units,Area of rectangle is L*b,Since the circle covers the breadth of rectangle,breadth =2r ,and since each one touches one end of the length of rectangle and passes through the centre of the other circle,the length is 2r+2r-r(the shared portion).

Hence l=3r,b=2r, Area of rectangle =6 r r,we have Pi.r r=10,hence area of rectangle =6 r r=6 10/Pi=60/Pi=60/22/7=60*7/22=19 roughly.

Awesome sir..... :)

Arslan Mishra - 6 years, 8 months ago

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