SWITCHING OLIVES
Tim’s mother has meticulously sorted the nibbles for tonight’s party so that there are 100 black olives in the black dish, and 100 green olives in the green dish. They look beautiful. Tim, however, thinks this is boring, so unknown to his mother he takes twenty green olives and puts them in the black dish. Then he mixes up the black dish and takes twenty of the olives in this mixture and puts them back in the green dish.
His mother is furious. ‘Now I’m going to have to sort them out. I don’t know whether there are more green olives in the black dish, or black olives in the green dish.’
Can you help?