Asymmetric pizza cut

Geometry Level 3

A circular pizza is cut in four sections as shown. The cuts are perpendicular to each other, and each cut divides the perpendicular diameter in a 2:1 ratio. There is a large piece of area A A , two medium-sized pieces of area B B each, and a small piece of area C C .

What is the areas A , B , C A, B, C , expressed as percentage of the entire pizza?

45.0%, 20.0%, 15.0% 49.4%, 21.5%, 7.7% 44.4%, 22.2%, 11.1% 30.9%, 27.5%, 14.1%

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.

3 solutions

Ahmad Saad
Mar 14, 2016

Otto Bretscher
Mar 14, 2016

Let's compute the area of the large slice on the top left, assuming unit radius, using only basic circle geometry (draw radii to the points where the cuts intersect the circle in the first and third quadrants):

(quarter circle) + (two sectors subtending an angle of arcsin ( 1 / 3 ) ) \arcsin(1/3)) + (two triangles) + (a square)

= π 4 + arcsin ( 1 / 3 ) + 2 2 9 + 1 9 1.55 =\frac{\pi}{4}+\arcsin(1/3)+\frac{2\sqrt{2}}{9}+\frac{1}{9}\approx 1.55

Expressed as a proportion of the total area, π \pi , this is about 49.4 % \boxed{49.4\%} .

Happy "Pi Day" to our Comrades in the USA!

PS: If the cuts were to intersect the diameter in a 99:1 ratio, this would be a good illustration on how the pie is distributed in the USA today ;)

Edit: See @ahmad saad ' s excellent illustation

Arjen Vreugdenhil
Mar 13, 2016

Calculating the exact percentages is challenging; see other solutions. However, it is not too difficult to pick the correct answer from the list given here. The trick is to construct a not-quite-circular pizza with the same area:

Each green section is one-quarter of a circle or an ellipse.

Suppose that the radius of the (original) pizza is 3, so that its total area is 9 π 9\pi . The pieces of the green distorted pizza then have areas 4 π 4\pi , 2 π 2\pi (twice), and π \pi , respectively; their total is 9 π 9\pi as with the original pizza, and the corresponding percentages are 44.4 % , 22.2 % , 11.1 % 44.4\%, 22.2\%, 11.1\% (one of the incorrect options).

Now simply observe that the smallest piece of our original pizza is completely covered by the smallest piece of the deformed pizza. Therefore the smallest percentage must be less than 11.1 % 11.1\% . The only option for which this is true is 49.4 % , 21.5 % , 7.7 % \boxed{49.4\%,\ 21.5\%,\ 7.7\%} .

I don't understand the geometry of your "not-quite-circular" pizza. You seem to assume that the cuts divide each other in a 2:1 ratio, but I don't think that is the case.

Otto Bretscher - 5 years, 3 months ago

Log in to reply

The cuts divide the circumscribed square into rectangles of 2x2, 2x1, 1x2, and 1x1. In each of these rectangles I inscribe a quarter circle or ellipse. Each of them takes up 1 4 π \tfrac14\pi of its rectangle, just like the total pizza does.

Arjen Vreugdenhil - 5 years, 3 months ago

Log in to reply

Yes, that makes sense now. If you do it this way, you don't really need all that fuss about the "not-quite-circular" pizza: It suffices to consider a quarter circle of radius 2 in the square on the bottom right.

Otto Bretscher - 5 years, 3 months ago

Log in to reply

@Otto Bretscher That's true. I liked the idea of applying it to all sectors and ending up with the same total area :)

Arjen Vreugdenhil - 5 years, 3 months ago

I make no assumptions about the ratio in which the cuts divide each other . It is true, of course, that this ratio is not exactly 2:1.

Arjen Vreugdenhil - 5 years, 3 months ago

0 pending reports

×

Problem Loading...

Note Loading...

Set Loading...