Ms Smart:Class begins. Sam,please give out the crayons.

Sam:All right.

Sam:…eleven,twelve,thirteen,fourteen,fifteen,sixteen,seventeen,eighteen,nineteen. There are only nineteen crayons.But there are twenty children in the class!

Ms Smart:I bought twenty yesterday.Did I lose one?

Amy:No,you didn’t.There’s one on the floor!

Amy:Oh no!

Sam:Oh,now there are twenty-one crayons!