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Summary:
Read the question.
Ask: "Out of which group?"
Use the total for that group.
Find the matching number (the overlap) to divide by that total.
How to Pay Attention to Probability Questions Using a Two-Way Table
When you're working with a two-way table, it's super important to understand what the question is asking and what total you're using to calculate the probability.
👉 Step 1: Read the question carefully.
Look for words like "given that" or "among those who..." These tell you which group you're focusing on.
👉 Step 2: Figure out your "total" (the denominator).
This is one of the most common mistakes. You're not always dividing by the overall total at the bottom of the table!
Instead, ask yourself:
Are they asking about everyone? (Use the grand total.)
Are they asking about a specific row or column? (Use the total for that row or column.)
Example: Watch the given video
👉 Step 3: Identify the part (numerator).
Now that you know the total group you're working with, find how many fit both conditions mentioned in the question.
Practice questions
There are five examples in this video.
For each question, pause the video and try to answer it on your own before checking the explanation.
This will help you identify any gaps in your understanding of how to calculate probabilities using two-way tables.
More practice questions visit the following site
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