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Yesterday, Granny had 12 cups and 10 matching saucers, but this morning she dropped a tray holding one third of the cups and half the saucers, breaking all of those on the tray.
How many of her cups are now without saucers if...
a) all of the cups are identical, and all of the saucers are identical?
b) the cups are all different to each other, and 10 of the cups matched a specific saucer?
If you liked this problem, here is an NRICH task which challenges you to use similar mathematical ideas.