Using numbers from 0 to 9 the number of 5 digit telephone numbers that can be formed is

The numbers 0,1,2,3,4,5,6,7,8,9 are 10 in number while preparing telephone numbers any number can be used any number of times.

This can be done in  $105$ways, but '0' is there

So, the numbers starting with '0' are to be excluded is  $94$ numbers.

 Total 5 digit telephone numbers =  $105- 94$ = 3439