Suppose you randomly choose a number between 10 and 20. What are the odds in favor of choosing a prime number?
There are 11 numbers between 10 and 20
How many of those are prime? 11,13,17,19
That leaves 7 that are composite
odds of prime are 4:7
How many of those are prime? 11,13,17,19
That leaves 7 that are composite
odds of prime are 4:7