SOLUTION: Find a counterexample to show that the following statement is incorrect: “The sum of any two odd numbers is divisible by 4”

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Question 120479: Find a counterexample to show that the following statement is incorrect:
“The sum of any two odd numbers is divisible by 4”

Found 2 solutions by stanbon, MathLover1:
Answer by stanbon(75887) About Me  (Show Source):
You can put this solution on YOUR website!
3+7=10 which is not divisible by 4
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Cheers,
Stan H.

Answer by MathLover1(20850) About Me  (Show Source):
You can put this solution on YOUR website!
show that the following statement is incorrect:

The+sum+of+any+two+odd+numbers+is+divisible+by+4."

first recall some of properties relating to odd numbers:
-All odd numbers can be expressed as 2n%2B1 where n is a whole number.
-Sum or difference of 2+odd numbers is always+even.
-Sum of odd+and even number is always+odd.

also recall that:

-A number is+divisible by 4, when the number formed by the last two right hand digit is divisible by 4.
-Or, a number is divisible by 4, if its two last digits are zeros or they make a two-digit+number, which is divisible by 4.

Any integer n can be put into one of the four cases 4q, 4q%2B1, 4q%2B2, and 4q%2B3.
Since 4q and 4q%2B2 are even, only the cases 4q%2B1 and 4q%2B3 need be considered.

SUPPOSE that x+is the EVEN number. Then x has a factor of 2 and x%5E2 has a factor of 4+; that is, x%5E2 is divisible by 4+.

If we choose two+odd numbers, let’s say 1 and 3, and add+their squares (1%5E2+%2B+3%5E2 in this case) we will find that the sum is not+divisible by 4.
1%5E2+%2B+3%5E2+=+1+%2B+9+=+10….10%2F4=+2.5…… => ..not+divisible by 4.

If+a and b are both+odd they have the form a+=+2+x+%2B+1 and b+=++y+%2B+1.

Then , which has a remainder of 2 when divided by 4 and so can not be equal to x%5E2, which is exactly divisible by 4.

Therefore the ASSUMPTIONthat x is EVEN is INCORRECT.
Since we+showed that one+of the terms MUST+be+even, one of a and b MUST+be+even, and the+other+odd.