In this lesson:
By the end of this lesson, you will be able to:
Probability is a number from 0 to 1 (inclusive).
On the SAT, probabilities appear as fractions, decimals, or percents.
A bag has 4 red, 3 blue, and 5 green marbles. One is drawn at random.
What is ?
Key: "From what group am I selecting?" — that group's total is your denominator.
Selected from all 200:
Same table, selected from all 200:
Find . Think before advancing…
Use when is simple but counting "not A" is tedious.
Example: Die roll.
Subtract the overlap — it gets counted twice otherwise.
Cannot happen simultaneously →
Example: Die.
From the survey table (200 students):
Event A and Event B are mutually exclusive. , .
Think before advancing…
For every SAT probability question from a table:
The hardest part is identifying the correct denominator.
Survey of 150 workers:
Selected at random:
Same table, selected at random:
Direct:
Complement:
Both give .
250 students: Smartphone(140) / Laptop(110). Grade 11 = 100, Grade 12 = 150. Grade 11 Laptop = 40.
Pause and work each before advancing.
1.
2.
3.
Wrong denominator is the #1 SAT trap
Forgetting to subtract overlap → answer too large
Next lesson: Conditional Probability
You will learn:
Conditional probability uses the same tables — just a different denominator.
Click to begin the narrated lesson
Basic probability of single events