Answer:
*add*
first lets take and example using 0.1 and 0.2
0.1
+0.2
=0.3
p/s : make sure the decimal points are alligned
*subtract*
we use the same rule as the above make sure the decimal point are alligned
0.2
-0.1
=0.1
*mutiply*
first vanish the decimal points
example 0.2 becomes 2.
if 0.9 becomes nine
then after you mutiply it, put the decimal point back where it should be
hope this helps! have a good day :)