Hi,
If you just want to count the 4 digit combinations possible using 09
then you can do it this way.
You can choose the first digit from 09, so there
are 10 choices. Once you have chosen the first digit, you can choose
the the second
digit from 09, 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 09, 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 fourthousand 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 ninehundred and nintynine
9999
Penny
