1. Show that there are infinitely many solutions in positive integers to a2 + b5 = c3.
2. Find the sum of all positive integers which have n 1s and n 0s when written in base 2.
3. Show that the midpoints of all chords of a circle which pass through a fixed point lie on another circle.
4. Can ten distinct numbers a1, a2, b1, b2, b3, c1, c2, d1, d2, d3 be chosen from {0, 1, 2, ... , 14}, so that the 14 differences |a1 - b1|, |a1 - b2|, |a1 - b3|, |a2 - b1|, |a2 - b2|, |a2 - b3|, |c1 - d1|, |c1 - d2|, |c1 - d3|, |c2 - d1|, |c2 - d2|, |c2 - d3|, |a1 - c1|, |a2 - c2| are all distinct?
5. An equilateral triangle side n is divided into n2 equilateral triangles side 1 by lines parallel to its sides. How many parallelograms can be formed from the small triangles? [For example, if n = 3, there are 15, nine composed of two small triangles and six of four.]
To avoid possible copyright problems, I have changed the wording, but not the substance, of the problems.