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(12) proportion & the number, 1, 2, 3, 4, 5, 6, or the numbers 1, 2, 3, 5, 7, 9, & c are in arithmetic progression: for which some use the mark image. Hence [[unclear] 9, 12, 15, 18, 21, 24. denotes that these numbers are in arithmetic progression.

68. If ratio is said to be unclear of other ratios, when it is produced by multiplying the exponents of those ratios together. For instance, let a be double of b, & c triple of d; then if f is both double & triple of g; that twice triple, or thrice double or sextuple, this last ratio will be compounded of the other two, that is f/g = ac/bd. In like manner the ^ addition underline ratio /underline /addition of 12 to 15 or of 4 to 5 is compounded of the ratio of 3 to 5 & of 4 to 3; because 12/15 = 3/5 x 4/3. So likewise the ratio of 1 to 2, is compounded of the ratios 2 to 3, & of 3 to 4: for 1/2 = 2/3 x 3/4 = 5/12. deletion unclear /deletion ^ addition underline also /underline /addition the ratio : to 2, is compounded of the ratios 4 to 5, 5 to 6, & 3 to 4: for 4/5 x 5/6 x 3/4 = 60/120 = 6/12 = 1/2.