RenB
Given that m is an integer, Is (m) (m + 1)(m + 2) divisible by 24?
(1) Units' digit of 2^m is a prime number
(2) Units' digit of 3^m is the smallest odd prime number
When should be m(m+1)(n+2), that is product of three consecutive numbers be multiple of 8?
a)
m is even.
We can be sure that the product is multiple of 3.
We can also be sure that the product is multiple of 8, as m and m+2 are even and one of them is multiple of 4 for sure .
b)
m is odd.
Again, the product is multiple of 3.
However, the product will be multiple of 8, only when m+1 is multiple of 8.
(1) Unit digit of \(2^m\) is a prime number
Unit digit of consecutive powers of 2 are 2,4,8,6,2,4.....
Here, digit 2 is prime and repeats at powers of 1, 5.....4k+1
Substitute m as 4k+1 => \((4k+1)(4k+2)(4k+3)=(4k+1)*2(2k+1)*(4k+3)=(odd)*(2*odd)*(odd)\). Thus the product will be multiple of 2 but not 4 or 8.
Answer is no as m is multiple of 6 but not of 24.
Sufficient
(2) Units' digit of 3^m is the smallest odd prime number
Unit digit of consecutive powers of 3 are 3,9,7,1,3,9.....
Here, digit 3 is smallest odd prime and repeats at powers of 1, 5.....4k+1
Substitute m as 4k+1 => \((4k+1)(4k+2)(4k+3)=(4k+1)*2(2k+1)*(4k+3)=(odd)*(2*odd)*(odd)\). Thus the product will be multiple of 2 but not 4 or 8.
Answer is no as m is multiple of 6 but not of 24.
Sufficient
D
thank you for providing the solution above. Can you please explain how the answer will be D when we can take 1 as the value of m given it will satisfy both the equations? If we take m=1, then, the equation will not be divisible by 24 whereas when we take m=5 (the next possible value), the equation will be divisible by 24. Should the answer not be E in this case?