Mindbender

A: "Careful, now," Ann warned the boy, handing him the paper bag. "You get 5p each for returning the empties, and full bottles are 31p each. Get litres, remember, the same as these."

"Fine, Mum," Sam replied. "But how many empties did you put in?"

"Oh not many – there can't be more than ten there," Ann told him. "And here's 68p, the difference you'll have to pay."

How many full bottles did Sam have to buy?

B: Lorna observed the drinking habits at Molly's party. "One fifth of us took both milk and sugar in our tea, two thirds had no sugar and three quarters of us took no milk. I forget how many took neither, but it was around forty."

How many had their tea without milk?