Commonly Confused Words: amount vs. number

[green-grrl.livejournal.com]

Today's commonly confused words are amount and number. Both refer to quantity, but which should be used when?

For example, should Harry Potter say, "I can't believe the amount of people crammed into the common room for this party" or "I can't believe the number of people crammed into the common room for this party"?

( Hermione and Professor Snape can help explain. )