The phrase “selected from among” signals conditional probability: the selection is limited to a smaller group. Use that group’s total as the denominator, then count the students who meet the target within it. Read those counts from the table and reduce the fraction. Using the overall total answers a different question.
Hints
- Hint 1
The phrase from among is a condition: it limits which students could be selected. Find the column for that workshop. What number at the bottom gives the total for that group?
- Hint 2
The numerator counts the students you want within the allowed group. Find where the bus row crosses the workshop column. Which count belongs above the column total?
Step-by-step
Use the robotics column
Step 1Choose the group being sampled
The student is selected from among the robotics students, so only that column contains possible selections. Its total is , so is the denominator, not the total of students at the fair.
- Step 2
Count the bus riders in that group
The bus row crosses the robotics column at . That means of the possible selections take the bus, so the probability is favorable selections divided by possible selections: .
- Step 3
Reduce the probability
Type in Desmos. It shows ; tap the fraction button to see . So the probability that a selected robotics student takes the bus is . Choice B.