The expression is
5x + 5y
We are to prove that it is an odd integer when x and y are integers of opposite parity
First, we can assume
x = 2a (even)
y = 2b + 1(odd)
subsituting
10(a + b) + 5
5 [(2(a + b) + 1]
The term
2(a + b) + 1 is odd and the result of an odd number multiplied by an odd number is odd
