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chetan2u VeritasKarishma
6 has 2 divisors: 2 and 3.... Now 2 and 3 can have same colours or diff colours..If both have same colours then we can have 2 options for 6....and if they have different colours then we have 1 option for 6....So we can have either a 3x3x2 or a 3x3x1 combination for{ 2,3 and 6}....Please explain where am I going wrong
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chetan2u VeritasKarishma
6 has 2 divisors: 2 and 3.... Now 2 and 3 can have same colours or diff colours..If both have same colours then we can have 2 options for 6....and if they have different colours then we have 1 option for 6....So we can have either a 3x3x2 or a 3x3x1 combination for{ 2,3 and 6}....Please explain where am I going wrong


You are wrong in counting..
Let us tak eth etwo cases..
(1) when all 3 are different = 3*2*1
(2) When both 2 and 3 are same,..
so they both can take any of three colours, and 6 will take any of the remaining color, so 3*2...
You cannot write this as 3*3*2, because the 3 in each case has to be same, it will be 3*1*2
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Thank you...I got it
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TyrionLannister
How many ways are there to paint each of the integers 2, 3,...,9 either red, green, or blue so that each number has a different color from each of its proper divisors?

(A)144
(B)216
(C)256
(D)384
(E)432


2, 3, 5 and 7 are prime numbers so there are 3 ways of choosing a colour for each of them.
2 and 3 could be same colour or different colours.
In case they are the same colour, there are 3*1*3*3 ways of choosing the colours for 4 numbers. In this case, there are 2 options for 6.
In case they are different colours, there are 3*2*3*3 ways of choosing the colours for 4 numbers. In this case there is 1 option for 6.
So in either case, there are 3*1*3*3*2 ways of choosing the 5 numbers. This gives is 3*1*3*3*2*2 = 108

4 should not be the same colour as 2 so there are 2 ways of choosing a colour for it.

8 should not be the same colour as 2 and 4 so there is only 1 way of choosing a colour for it.

9 should not be the same colour as 3 so there are 2 ways of choosing a colour for it.

Total number of ways of choosing colours for all 8 numbers = 108*2*1*2 = 432

Answer (E)
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VeritasKarishma

Gracias!
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