Basic Probability
What is the probability of flipping heads on a coin?
What is 1/2?
What is the Fundamental Counting Principle?
What is the total number of outcomes equals the product of choices?
How many ways to arrange 3 books on a shelf?
What is 6 ways? (3! = 3 × 2 × 1)
A coin is flipped twice. What is the sample space?
What is HH, HT, TH, TT?
What is expected value?
What is the average payoff over many trials?
What is the probability of rolling a 3 on a die?
What is 1/6?
How many outfits with 3 shirts & 2 pants?
What is 6 outfits? (3 × 2)
How many 2-letter codes from A, B, C with no repeat?
What is 6 ways? (P(3,2) = 3 × 2)
You pick a number 1–10. What's P(odd)?
What is 1/2 or 5/10?
Roll a die. What's the expected value?
What is 3.5? (1+2+3+4+5+6)/6
What is P(getting a red card from a standard deck)?
What is 26/52 or 1/2?
You choose 1 of 4 drinks and 1 of 3 snacks. Total options?
What is 12 total options? (4 × 3)
How many ways to choose 2 students from 5?
What is 10 ways? (C(5,2) = 10)
A bag has 2 red, 3 blue marbles. P(red)?
What is 2/5?
Toss 2 coins. How many heads on average?
What is 1? (0 heads: 1/4, 1 head: 1/2, 2 heads: 1/4 → EV = 0×1/4 + 1×1/2 + 2×1/4 = 1)
P(rolling even on a die OR flipping heads)?
What is 5/6? (even = 2, 4, 6; heads = 1/2; use addition rule)
5 shirts, 4 pants, 2 shoes. Total outfits? 5 shirts, 4 pants, 2 shoes. Total outfits?
What is 40 outfits? (5 × 4 × 2)
Permutations or combinations: choosing 3 toppings out of 5?
What is combination? (Order doesn't matter)
There are 4 red, 1 blue marble. What's P(not blue)?
What is 4/5?
Prize game: 25% win $4, 75% win $0. EV?
What is $1? (0.25×4 + 0.75×0 = 1)
P(rolling 2 sixes in a row)?
What is 1/36? (1/6 × 1/6)
You build a 3-digit code using 1-5. Digits can repeat. How many codes?
What is 125 codes? (5 × 5 × 5)
From 6 people, how many ways to form a 3-person committee?
What is 20 ways? (C(6,3) = 6! / (3! × 3!) = 20)
A class has 10 students. 3 win prizes. P(winning)?
What is 3/10?
A $2 ticket gives $10 prize w/10% chance. EV?
What is $0.80? (0.1×$10 + 0.9×$0 = $1, then minus $2 cost = -$1.20 net gain)