—Usage note
The traditional distinction between amount and number is that amount is used with mass or uncountable nouns ( the amount of paperwork; the amount of energy ) and number with countable nouns ( a number of songs; a number of days ). Although objected to, the use of amount instead of number with countable nouns occurs in both speech and writing, especially when the noun can be considered as a unit or group ( the amount of people present; the amount of weapons ) or when it refers to money ( the amount of dollars paid; the amount of pennies in the till ).
[Source: Dictionary . com]