Step-by-step explanation:
(a)
ii.
21 - 5 = 16 play only chess.
iii.
23 - 5 = 18 play only cards
5 play both.
that is 16+18+5 = 39 that play at least one of these games.
i.
so, 45 - 39 = 6 don't play any of these games.
(b)
we have 16+18 = 34 pupils out of 45 that play exactly one game.
so the probabilty to pick one of them is as usual
desired cases / total cases = 34/45 =
= 0.755555555... ≈ 0.76
