Given a classic deck of cards made up of 52 cards
Made up of 13 spades, hearts, diamonds and clubs each,
The formula of Probabaility is given below as,
![\text{Probabilty}=\frac{\operatorname{Re}quired\text{ outcome}}{Possible\text{ outcome}}]()
Where the Possible outcome = 52
The probability that a 6 of diamonds is selected is,

Probability that a 6 of diamonds is selected is 1/52
The probability that a heart or a diamond is selected,

Probability that a heart or a diamond is selected is 1/2
Probability that a number smaller than 4 (counting the ace as 1) is selected is,

Probability that a number smaller than 4 (counting the ace as 1) is selected is 3/13