Collier's New Encyclopedia (1921)/Arithmetical Mean

ARITHMETICAL MEAN. (1) The number, whether it be an integer or a fraction, which is exactly intermediate between two others. Thus, 5 is the arithmetical mean between 2 and 8; for 2 + 3 are = 5,and 5 + 3 are = 8. To find such a mean add the numbers together and divide their sum by 2; thus, 2 + 8 = 10, and 10 ÷ 2 = 5. (2) Any one of several numbers in an arithmetical ratio interposed between two other numbers. Thus, if 6, 9 and 12 be interposed between 3 and 15, any one of them may be called an arithmetical mean between these two numbers.