# A problem by Josh Rowley

Xavier has 1000 coins and Yvonne has 999 coins. Let *x* denote the number of tails face up on Xavier's coins and *y* denote the number of tails face up on Yvonne's coins. The probability that \( y\ge x \) can be expressed as *a/b* where *a* and *b* are positive coprime integers. What is *a* + *b*?