$begingroup$ For (a), An easy way to look at is that you've got lowered your likelihood House to just the combos that have at least one boy: This is actually the very same probability of flipping a fair coin 8 occasions and having 7 heads. It truly is quite unlikely. https://sites.google.com/view/pg-in-sector-15-gurugram/book-modern-pg-for-boys-in-gurgaon