Generating 2 characters randomly in Mac Numbers

My student struggles with dyslexia. I created a grid in Numbers in which I filled in all the cells with either "f" or "g." To do so I typed in CHAR RANDBETWEEN 102, 103. It worked perfectly since the corresponding ASCII numbers are only one apart. He has to read a few f's following by a g, then a couple more f's, then several g's.

Now I want to do the same thing with "i" and "l," but their ASCII codes are 105 and 108. Using the above formula, I end up with a lot of "j" and "k" in the mix, which isn't helpful. Can anyone suggest a solution? I've tried a few things but keep getting a syntax error.

I realize that I'm probably using the wrong lingo when I write "formula" but this is definitely not my field. Thanks for your help!