GmatPrep3

[saurabhmahajan]

rs+r =odd

so by rule odd +even =odd
so rs must be odd and r should be even
for rs to be odd r and s should be odd
when both are odd then r+s= even.

but i got it worng

[nithi_mystics]

rs+r = odd

r(s+1) = odd

therefore r and s+1 should be odd.

since s+1 is odd, s should be even