Or - Event A or event B
CONCEPTS
Equation
• Probability 1 Event Occurs =
Number of desired events / Total number of possible events +
Number of desired events / Total number of possible events +
Number of desired events / Total number of possible events
Tips
• Always look for the word "or“, or the phrase "what is the probability of x happening“.
• If there is a common event between the 2 desired events, then the probability of that event occurring needs to be subtracted from the total probability.
PRACTICE PROBLEMS
Question 1 Each ball is numbered (Red has numbers 1,2 Green has numbers 1,2,3 Yellow has numbers 1,2,3,4). What is the probability the ball is yellow or is number 2?
-- Answer -- 4/9 + 3/9 - 1/9 = 6/9
Add all of the balls that are yellow (4/9) + add all of the balls that are number 2 (3/9) and subtract the ball that is yellow AND number 2 (1/9)
ACT PRACTICE PROBLEMS
