The simple and quick method of the multiplication

Abstract

With respect to the multiplication between the two digit numbers and ab and ac, or and b+c =10 or ab, and, the paper respectively proposes theorem 1 and theorem 2. According to these two theorems, the results of the multiplications can be obtained by the simple mental arithmetic. Moreover, the paper presents some examples of multiplication in order to verify that both of the theorem 1 and theorem 2 are correct and applicable.