Eduqo
Quantitative Aptitude›Ch 5: Data & Speed Maths›Probability Basics
Master coins, dice, cards & complementary events for competitive exams
Probability is the ratio of favorable outcomes to total possible outcomes. Its value always ranges from 0 to 1, where 0 means an impossible event and 1 means a sure event. The sum of probabilities of all possible outcomes is always equal to 1.
Quick Memory Hooks
| Suit / Category | Color & Count | Face Cards |
|---|---|---|
| Spades (हुकुम) | Black (13) | 3 (J, Q, K) |
| Clubs (चिड़ी) | Black (13) | 3 (J, Q, K) |
| Hearts (पान) | Red (13) | 3 (J, Q, K) |
| Diamonds (ईंट) | Red (13) | 3 (J, Q, K) |
Coin Flip
(Head or Tail)
Head or Tail
Probability of getting a head is 1/2.
Single Die
(Numbers 1 to 6)
Numbers 1 to 6
Probability of rolling an even number is 3/6 = 1/2.
Face Card
(Jack, Queen, King)
Jack, Queen, King
Total face cards in a deck are 12 out of 52.
Complement
(Not Happening)
Not Happening
If P(E) is 0.3, then P(not E) = 1 - 0.3 = 0.7.
Probability can be negative or 1.5Probability is always between 0 and 1
Exam trap: Values less than 0 or greater than 1 are mathematically impossible.
A deck has 16 face cardsA deck has 12 face cards (J, Q, K)
Exam trap: Aces are NOT face cards; they are ace cards.
Sum of P(E) and P(not E) is 0Sum of P(E) and P(not E) is always 1
Exam trap: An event either happens or it does not happen, totaling 100%.
Q1.What is the probability of getting a sum of 8 when two fair dice are rolled simultaneously?
Q2.If a card is drawn from a well-shuffled pack of 52 cards, what is the probability that it is a red face card?