new math

Noun

 * 1)  A dramatic and short-lived change in the teaching of mathematics in grade schools in the 1960s, focusing on abstract topics such as symbolic logic, to the detriment of simple arithmetic etc.
 * 2)  The methodology used to arrive at an unreasonably incorrect answer for a mathematical calculation.
 * She quickly calculated the tip to be $45.00 on the restaurant tab of $110.50, apparently using new math.