Difficulty: easy-schmeasy, if you subtract. More complicated if you try to add.
Problem 25 = 5².
(I wonder how often you can switch the digits and still write an equivalent expression.)
Difficulty: Medium. More damned logarithms, but there's a neat little prime factorization going on, too.
Standard instructions for this series: No calculator allowed. Express answers in reduced form. Rationalize denominators. Radicals must be reduced. All numbers are base ten unless otherwise specified. Do not approximate radicals or π. Leave such answers as 1025π or √39, for example. Source: UVM Math Contest
answer 17 and answer 25.