$100$ cards are numbered from $1$ to $100$. Find the probability of getting a prime number.

Given: $100$ cards are numbered from $1$ to $100$

To do: To find the probability of getting a prime number. 

Total number of cards $=100$

Prime numbers between $1$ and $100=25$

Probability of getting a prime number $=\frac{Number\ of\ favourable\ outcomes}{Number\ of\ total\ outcomes}$

$=\frac{25}{100}=\frac{1}{4}=0.25$

Thus, the probability of getting a prime number is $0.25$.