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(16) proportion, 3, 5, 7, the sum of the extreems is 3 + 7 or 10 which is double of 5 the mean term. In general any continued arithmetic proportion may be denoted thus, formula where the sum of the extremes will always be formula, which is double the mean, a + d

74. This mean term is called an underline arithmetical mean /underline between the two extremes. Hence to find an arithmetical mean between two quantities you need only take half their sum.

75. In a continued geometric proportion the product of the extremes is equal to hte square of the mean term. Thus in the continues proportion, 2:6::6:18, deletion the product of /deletion the product of the extremes 2 x 18, is 36, & the square of the mean 6 is also 36.