1. Lop 5a mua mot so vo. Neu moi ban mua 4 quyen thi thua 90 quyen. Neu moi ban mua gap ruoi thi vua het . Hoi lop 5a mua bao nhieu vo
2. Mot don vi bo doi muon sang song . Neu 1 thuyen cho 20 nguoi thi 16 nguoi khong duoc sang song. Neu 1 thuyen cho 12 thi 24 nguoi chua duoc sang song . Hoi don vi bo doi do co bao nhieu nguoi.