So I'm trying out the test to prepare me for my upcoming cambridge interview, there is one problem I can't understand though this one: 44 Sally is helping her father dig worms for fishing. "That's exactly enough," he says as she places a worm in his tin. "How many do you need?" she enquires. "I use 4 worms on my hook and reckon on having to replace an average of one of these each time I cast. I cast 12 times an hour. Today I will fish 5 pools spending an hour at the first 4 and an hour and a half at the fifth. I always discard the worms on my hook when walking between pools." How many worms are in the tin? A 66 B 69 C 81 D 86 E 264 I reckon it is D since: He passes five pools thus 4*5 worms should be placed on the hook. He spends a total of 5.5 hours at the pools netting 12*5.5=66 throws --> 66 worms. 66+20=86 worms It is possible that they mean an hour total on the first four pools in this case: Passes five pools = 20. spends 2.5 hours casting = 12*2.5=30 casts --> 30 worms. 20+30=50 worms. According to the answer sheet the answer is C. It should have something to do with 5 pools since 86-5=81 but what?