How to calculate the slope of 1:1.2 or 1:1.5

How to calculate the slope of 1:1.2 or 1:1.5

1: The slope of 1.2 means that the tangent value of the slope angle is 1:1.2 = 5 / 6;
1: The slope of 1.5 means that the tangent value of the slope angle is 1:1.5 = 2 / 3