You are aware that as far as Excel is concerned, "90%" and 90% are not the same thing, right?
These 2 formulas are not equivalent:
=IF(B3/E3<0.9, B3/E3, "90%")
=IF(B3/E3<0.9, B3/E3, 90%)
The first formula will put the text string 90% in the cell, while the second will put the numerical value 0.9 in the cell, which can then be formatting to display the numerical value 90%.
This may or may not matter, depending on how you plan to use the 90%, but what you are in fact doing is putting a number in the cell when the IF function evaluates the TRUE condition (B3/E3), but a text string when the IF evaluates to the FALSE condition of "90%".
Unless you specifically need the 90% to be a text string, many would consider your use of the quotes to be incorrect.
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