I am importing data from my on-line bank account and Excel is treating numbers as text.

Often, when you import (or copy/paste like you did) excel converts numbers to text. Formatting will not change that, as Formatting is a cosmetic change only, it has no affect on the underlying cell contents.

There are a few ways around this problem, a good 1 of which was suggested above.
Another way would be to incorporate a function into your formulas to do the conversion for you, but how you do that will depend on what formula or function you are using - we would need to see some examples.

One alternative option I use frequently is the Paste Special - Multiply method. What you do is put the number 1 anywhere in your workbook and copy the cell; then highlight all your 'text' numbers, go up to Paste Special > multiply. You are basically multiplying all of your text numbers by 1. This should turn them all to Number format.

Good option as well - you could do the same with ADD 0