Bunuel wrote:
f(x)=x^2−1. For which of the following values of x is f(x) divisible by 6?
A. 1812
B. 2721
C. 3118
D. 4245
E. 5653
A number is divisible by 6 when the sum of all of the digit is divisible by 3 and the number itself is EVEN.
Try to plugin value X and evaluate its UNIT DIGIT :
A. 1812 -> \((1812^2)-1\) --> the result is ODD, not the answer.
B. 2721 --> \((2721^2)-1\) --> the result is EVEN, can be the answer.
C. 3118 --> \((3118^2)-1\) --> the result is ODD, not the answer.
D. 4245 --> \((4245^2)-1\) --> the result is EVEN, can be the answer.
E. 5653 --> \((5653^2)-1\) --> the result is EVEN, can be the answer.
As we can see, only B, D and E left.
At this point, I chose to calculate E : \((4245^2)-1\) = 18020024, which sum all of the digits is not divisible by 3. E cannot be the answer.
stuck between B and E.
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