The quotient obtained by dividing the former term by the latter term is the ratio. For example, 3: 6 = 3 ÷ 6 = 0.5 and the ratio of 3: 6 is 0.5. The ratio can be an integer, a fraction or a decimal.

N1/na: N2/na = n1:N2, and the final result is a ratio, so it is not a ratio, but a simplified ratio.