Order decimals from least to greatest ... 1.09, 1.901,1.9,1.19

The easiest way to do this is to write the decimals with equal amount of places after the dot and you'll see it more clearly:

1.09 = 1.090

1.901 = 1.901

1.9 = 1.900

1.19 = 1.190

So from the least to the greatest:

1.090

1.190

1.900

1.901

In a form you gave at the beginning:

1.09 < 1.19 < 1.9 < 1.901