Geraldine is picking a four-digit password by using the digits 0 through 9. She can use each digit only once. How many different passwords are possible?

0-9 = 10 numbers 1st digit can be 1 0f 102nd digit can be 1 of 93rd digit can be 1 of 84th digit can be 1 of 7

10 * 9 *8*7 = 5040 different combinations