I have a data set containing XY coordinates of points. It's in Excel. I am very new to GIS and I have two questions regarding this data set.

Firstly, coordinates are said to be in WSG84, but have different decimal places lengths. Longest of them have 9 decimal places. They have 3 digits before decimal points. So a 9 digit coordinate is XXX.YYY.ZZZ or a 6 digit one is XXX.YYY. I want them all to be in decimal coordinate system. Is there way that I can do this automatically in Excel?

My second question is about importing these coordinates to ArcMap. When I try to convert the data to XY points, ArcMap disregards the decimals even though both the shape layer and the points layer are in WSG84 format. Thus, drawing the points to a totally unrelated space.