Chapter 3 - Section 3-5 - Discrete Uniform Distribution - Exercises - Page 79: 3-87

The probability that your number is called $=\frac{1000}{10000000}=0.0001$

let X be the random variable (seven-digit), then, $f(x)=\frac{1}{10000000},x=0, 1,...,9999999$ The probability that your number is called $=\frac{1000}{10000000}=0.0001$