The number of ways of choosing 4 digits from 10 digits without replacement ( order is important) is
. This is the number of all possible permutations of choosing 4 from 10. The first 4 numbers of your phone number is a unique 4 digit number(4 different digits). The required probability is

The answer is C. Use the quadratic formula to solve it and you should be just fine!
7/100
3/10
21/125
3/ 2500
7/50
I simplified them for you
Answer:
You did not include the price they bought the units at.
I will assume this price is $5.
= 5 * 1,000
= $5,000
Recording it will be:
Account Debit Credit
Merchandise Inventory $5,000
Accounts Payable $5,000