How many four-digit numbers can be formed from the digits 1, 3, 5, 7, 8, and 9 if the numbers are less than 9,000 and digits are not used repeatedly? (Hint: Begin with the digit where there is a restriction on the choices.)

Question

How many four-digit numbers can be formed from the digits 1, 3, 5, 7, 8, and 9 if the numbers are less than 9,000 and digits are not used repeatedly? (Hint: Begin with the digit where there is a restriction on the choices.) ​

Quizplus · Accepted Answer

The first digit has 5 options (1, 3, 5, 7, 8) since the number must be less than 9,000, excluding 9. For the second digit, there are 5 remaining choices (since one digit has been used already), for the third digit there are 4 choices, and for the last digit, there are 3 choices. Multiplying these together gives 5 * 5 * 4 * 3 = 300.

How Many Four-Digit Numbers Can Be Formed from the Digits