1. "We got the cakes, Mum," said Susan, as her brothers followed her into the kitchen. "Nice ones at 8p and 13p. All for 2 pounds and 40p." Linda looked. "Fine, but no more for you today," she declared. "I see you've eaten exactly half of them already." She was right, so how many had they bought?

20 cakes

22 cakes

18 cakes