A conditional probability asks for a chance within a group already known. The cue is a phrase such as selected from: find that group's total in the table, then find the count that also meets the requested description. Evaluate the resulting fraction in Desmos. Using the other row or column total answers a different question.
Hints
- Hint 1
The words selected from set the condition, or the group the visitor must belong to. Find the total for that group in the table. Is it a row total or a column total?
- Hint 2
For a conditional probability, the numerator counts visitors who meet both descriptions. Where do the bird-walk row and the used-station column cross?
Step-by-step
Restrict the table, then form the fraction
Step 1Find the group that could be selected
The visitor is selected from those who used the station. That's the condition, or what you already know about the visitor. The used-station column has a total of , so only those visitors belong in the denominator, not all visitors.
- Step 2
Find the count that also chose the bird walk
The bird-walk row meets the used-station column at . So visitors meet both descriptions: they used the station and chose the bird walk.
- Step 3
Write the probability
A conditional probability puts the count meeting both descriptions over the count in the known group:
The means “given that.” Using as the denominator would instead start with everyone who chose the bird walk.
- Step 4
Evaluate the fraction
Type in Desmos. It shows ; tap the fraction button to see . So the probability that a visitor known to have used the station chose the bird walk is . Choice D.