10. Let $ab$ be a two-digit number in decimal notation, and let $ba$ be the two-digit number formed by swapping the unit and tens digits, the product of these two two-digit numbers is 4930, find the values of $a$ and $b$.
10. Answer: $(a, b)=(5,8),(8,5)$. Hint: $(10 a+b)(10 b+a)=4930$.