The term 'putting two and two together, say' can be solved by the 10-letter word 'ARITHMETIC'. ARITHMETIC is a branch of mathematics that deals with the study of numbers, their properties, and the operations used to manipulate them. It is one of the oldest branches of mathematics, and is used in everyday life to solve problems such as addition, subtraction, multiplication, and division. By putting two and two together, one can use ARITHMETIC to solve complex mathematical equations.