Question

Consider a company that selects employees for random drug tests. The company uses a computer to randomly select employee numbers that range from 1 to 6857 6857. Find the probability of selecting a number divisible by 1000. Find the probability of selecting a number that is not divisible by 1000.

Answer 1

1≤1000n≤6857

0.001≤n≤6.857

1≤n≤6

So there are (6-1+1)=6 multiples of 1000 out of 6857-1+1=6857 numbers.

So 

P(1000n)=6/6857

...

The inverse probability is just 1-P(1000n)

P(!1000n)=1-6/6857

P(!1000n)=6851/6857