40 Years Old Algebra Equation Funny 40th Birthday Math Shirt Solid colors: 100% Cotton; Heather Grey: 90% Cotton, 10% Polyester; All Other Heathers: 50% Cotton, 50% Polyester Imported Machine wash cold with like colors, dry low heat Math humor birthday gift idea for math nerds A great shirt for anyone who is good at math Lightweight, Classic fit, Double-needle sleeve and bottom hem