Combinations
CONCEPTS
Equation
• C of single events: Cˣ₁ (put a 1 on the bottom and x on top)
• C of paired events: Cˣ₂ (put a 2 on the bottom and x on top)
etc
Tips
• The word, combination, is typically in the question
Definitions
• Combinations: The number of possible arrangements where order doesn’t matter
PRACTICE PROBLEMS
Question 1 A reservation number is composed of 5 digits. The digits can be any number from 0 - 9. The digits may repeat. How many possible 5 digit reservations numbers are there?
-- Answer -- 10 * 10 * 10 * 10 * 10
Question 2 12 students will play 2-person beach volleyball. What is the maximum number of different 2-person teams possible?
-- Answer -- 1/3
C¹²₂ = (12 * 11) / (2 * 1) = 132/2 = 66
Question 2 There are 10 people in line. What’s the number of combinations where person A can be 1st & person B can be 2nd?
-- Answer -- Combinations = (10)(9) / (2)(1)
ACT PRACTICE PROBLEMS
