SamzayWarrior
Bunuel
Bunuel
12 Days of Christmas 🎅 GMAT Competition with Lots of Questions & FunPablo wants to paint a cube, with each face being either blue or red. How many different ways can he paint the cube, if two cubes are considered different only when one cannot be reoriented to match the other?
A. 8
B. 10
C. 12
D. 32
E. 64
To achieve his task, Pablo can paint the cube in the following different patterns:
- Pattern 1: All 6 faces are red.
- Pattern 2: 1 face is blue and 5 faces are red.
- Pattern 3: 2 adjacent faces are blue and the other 4 faces are red.
- Pattern 4: 2 opposite faces are blue and the other 4 faces are red.
- Pattern 5: 3 faces that share the same corner are blue and the other 3 faces are red.
- Pattern 6: 2 opposite faces and 1 adjoining face are blue and the other 3 faces are red.
- Pattern 7: 2 adjacent faces are red and the other 4 faces are blue.
- Pattern 8: 2 opposite faces are red and the other 4 faces are blue.
- Pattern 9: 1 face is red and 5 faces are blue.
- Pattern 10: All 6 faces are blue.
Therefore, Pablo can paint the cube in 10 distinct patterns.
Answer: B.
chetan2u Bunuel KarishmaB GMATPillWhy is the solution not 2^6=64 (each of the 6 faces has 2 options)? How do we know when to use which approach?
Not able to understand why are we looking for pattern this way? Is this solution because of this part of the question- "if two cubes are considered different only when one cannot be reoriented to match the other"? Also is there any other easy way to visualize this? Not able to figure out this solution
We could use 2^6 if all faces were distinct, say in case of a die. Each face of the die has a number from 1 to 6 written on it. Now we could paint the 1 number face red or blue, the 2 number face red or blue etc. So here we can paint in 2^6 ways.
But a regular cube has all identical faces so we end up enumerating. With identical spots, often enumeration is required.
Yes, this part ("if two cubes are considered different only when one cannot be reoriented to match the other") tells us that say we paint the top face red and all other blue and in another case, we paint the bottom face red and all other blue - they are the same case and should be counted once only. The faces are to be considered identical because we can pick the first cube and put its top face down to give us the second case. So essentially, the faces are identical.