mathhothouse.me
Pre-RMO — training
Problem 1: If a, b, c, and d satisfy the equations $latex a+7b+3c+5d=0$ $latex 8a+4b+6c+2d=-16$ $latex 2a+6b+4c+8d=16$ $latex 5a+3b+7c+d=-16$ then what is the numerical value of $latex (a+d)(b+c)$?…