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Probability.......Average


Centrino
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Centrino .. where did you get this question.. seems to be HARDDDDDDDDDDDDDDDD BIN ...

 

struggled for sometime but think this is the approach... i got the answer with this approach..

 

the 9 numbers are

3 are in the form 3n ( multiples of 3) ---- SET 1

3 are in the form 3n+1 ---- SET 2

3 are in the form 3n+2 ---- SET 3

 

if you take the 3 numbers from the same set then the sum is divisible by 3 ..

so we got 3 combinations here for 3 sets ..

the only other way is taking 1 from each set ... so 3C1 * 3C1 * 3C1 = 27

[ this is like 3n + 3n+1+3n+2 = 9n+3 which is divisible by 3]

so total combinations = 3+27 = 30

 

probability = 30/84 = 5/14

 

D

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