Hi,

If you just want to count the 4 digit combinations possible using 0-9 then you can do it this way.

You can choose the first digit from 0-9, so there are 10 choices. Once you have chosen the first digit, you can choose the the second digit from 0-9, and thus there are 10 ways to choose the second digit for each choice of the first digit. Hence there are 10  10 = 100 ways to form a two digit combination.

Once you have a two digit combination you can choose the third digit from 0-9, so for each 2 digit combination there are 10 choices for the third digit. Thus 100  10 = 1000 possible 3 digit combinations.

Continue.

If you want to list all the 4 digit combinations then do so in an orderly way. One way is to think of each 4 digit combination as an integer with possibly leading zeros. That is think of 4302 as four-thousand three hundred and two and 0013 as thirteen.Hence you can list them as follows.

The samllest is zero
0000

then one
0001

and two
0002

eventually ten
0010

and one hundred
0100

The largest is nine-hundred and ninty-nine
9999

Penny

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