The 5-digit number 5228X is a multiple of 6. What digit is represented by X?
+333 5+2+2+8 = 17 so x can be 1 or 8 (if you want to know if a big number is divisable by a small number than you can add all the digits together but it does not always work)
In order for a number to be divisible by 6, it needs to be divisible by both 3 and 2.
The divisiblity rule for 2 is if the end digit is an even number.
The divisiblity rule for 3 is if all the digits added up together can be divided by 3.
Even numbers are easy to spot, so let's focus on divisibility by 3.
5+2+2+8+X = 3n
17+X=3n
Now, we can use trial and error.
Case 1: n=6
17+X=18
X=1, which is not an even number, so discard this solution.
Case 1: n=7
17+X=21
X=4, which is an even number, so this is a valid solution.
At this point, we don't have to test for n=8 because the question states that there is only one digit for X.
So the answer is X=4.
+9519 That means 5228X is divisible by 2 and 3.
So X must be an even number, and \(5 + 2 + 2 + 8 + X\) is divisible by 3.
But that means \(2 + 2 + 2 + 2 + X \) is divisible by 3. Taking mod 3 again on both sides,
\(2 + X\) is divisible by 3, and don't forget that X is an even digit.
\(X = 4\) is the only possible solution.
