$begingroup$ For (a), A straightforward way to have a look at is that you've lowered your probability Area to only the combos that have not less than one boy: Therefore, the capitalized Greek letter $text N$ (Nu) wouldn't be italicized and may be visually indistinguishable from capital Latin letter N. https://share.evernote.com/note/3862b16f-f83a-cbec-2fb6-07ed32465225