A Maths Dictionary for Kids Quick Reference is a device friendly html version with definitions and detailed examples for over 950 math words and terms.
The statistics about the average cost of a haircut vary, but a few years ago American Salon, a publication for beauty industry professionals, reported the numbers as $21 for a cut in a salon with fewer than 6 chairs, and $44 for a salon with more than 13 chairs.
My haircuts are about $12-13 and I always tip $2. I have no relationship and don't expect anything, I just think it's a profession that you tip. Like some other tips, I always give the tip to the hairdresser in cash rather than on my card, so they can decide how to chalk it up. I normally tip $1-2.