I'm guessing the fields are not coming in as numeric but as text fields. The fix is to make sure your data are numbers and are formatted as numbers. You may have to close ArcMap and reopen it for the file to be reloaded after you fix the Excel file so the data in the field look like numbers.
(Great example of why Excel is a helpful analysis tool -- but a terrible database.)
(Please use the "move" function (at right) to move this thread to the Managing Data space. You posted in the GeoNet Help space, which is for questions about the GeoNet site, not using ArcGIS.)