We will first find the probability that we call a number which does not have zeros.

We have \(\displaystyle{10}^{{4}}={10000}\)

numbers to choose from (on each of the 4 places we can put any of the 10 digits). Also, we have \(\displaystyle{9}^{{4}}={6561}\)

numbers which do not have a zero (because on each of the 4 places we can put any of the 9 digits - we must exclude 0).

So, the probability is

\(\displaystyle\frac{{6561}}{{10000}}={0.6561}\)

We have \(\displaystyle{10}^{{4}}={10000}\)

numbers to choose from (on each of the 4 places we can put any of the 10 digits). Also, we have \(\displaystyle{9}^{{4}}={6561}\)

numbers which do not have a zero (because on each of the 4 places we can put any of the 9 digits - we must exclude 0).

So, the probability is

\(\displaystyle\frac{{6561}}{{10000}}={0.6561}\)