Number of circular permutations with coloring

MathematicsCombinatoricsHard

Published:

24. A circle is divided into six equal sections. Each section is to be coloured with a single colour so that three sections are red, one is blue, one is green, and one is yellow. Two circles have the same colouring if one can be rotated to match the other. In the diagram, Figure 1 and Figure 2 have the same colouring, while Figure 1 and Figure 3 have different colourings. How many different colourings are there for the circle? (A) 14 (B) 12 (C) 24 (D) 10 (E) 20

This question includes visual content: The image shows three separate circles, each divided into six equal wedge-shaped sections. The circles are labeled 'Figure 1', 'Figure 2', and 'Figure 3'. Each circle has its sections colored in specific patterns: two 'red', one 'blue', one 'green', and one 'yellow'. Figure 1 and Figure 2 show different arrangements that are considered identical under rotation. Figure 3 shows a different configuration.

Animated Video Solution

The first half plays free, the full solution is in the app.

Step by Step Written Solution

1
Step 1

In this problem, we need to find the number of unique ways to color a circle divided into six equal sections. We are given two red sections, one blue, one green, and one yellow. However, wait, the problem says two circles are the same if one can be rotated to match the other. Let's re-read the count: two are red, one is blue, one is green, and one is yellow. Actually, looking at the totals, five sections are colored and one is left unspecified in text, but let's check the images. Figure one has two reds, a blue, a yellow, and a green. That is five colors for six spots... wait, let's look closer. It says three sections are red. Let's re-read carefully: three sections are red, one blue, one green, and one yellow. Total of six.

Permutations with Rotational Symmetry

Total Sections: 6

Colors: 3 Red (R), 1 Blue (B), 1 Green (G), 1 Yellow (Y)

2
Step 2

Since rotations make two colorings equivalent, we can use a strategy where we fix the position of the non-red colors relative to the red ones. Let's find all the ways the three red sections can be arranged first.

$$\text{Patterns of Red sections (R):}$$
3
Step 3

Case one: The three red sections are all next to each other. We can represent the circle as a string of six slots.

4
Step 4

In this case, we have three empty slots left for Blue, Green, and Yellow. Since the red block is fixed, these three sections can be arranged in three factorial ways.

$$3! = 3 \times 2 \times 1 = 6 \text{ ways}$$
5
Step 5

Case two: Two red sections are adjacent, and the third one is separated by one or two slots. Let's look at the arrangement R R space R space space.

6
Step 6

This configuration is distinct from the first because the reds are no longer all clumped. Again, we have three distinct spots left for Blue, Green, and Yellow.

$$3! = 6 \text{ ways}$$
7
Step 7

Is there another way? What if the third red is two spaces away? That would be R R space space R space. Notice that this is the mirror image of the previous case, but remember only rotation is allowed for equivalence, not reflection unless specified. However, the problem says 'rotated to match'. Let's check rotation.

8
Step 8

If we rotate R R x x R x, we cannot get R R x R x x. These are distinct under rotation. So this gives another six ways.

$$3! = 6 \text{ ways}$$

The rest of this solution is on Solvi

8 more steps are locked. Watch the full animated, narrated solution for free.

Snap a photo, solve any question like this.

Download on the App Store Get it on Google Play

Free to download · First solutions are on us

100K+Questions solved daily
50K+Students learning
4.8 ★App Store rating

About This Question

Subject
Mathematics
Topic
Combinatorics
Difficulty
Hard
Question Type
Multiple Choice

Solve any question in seconds

Snap a photo and AI explains it step by step with voice and animation.

Download on the App Store Get it on Google Play
Solvi
The full solution is in the appFree to download · First solutions are on us
Get