A collection has \(40\) labeled objects: \(18\) in category A, \(12\) in category B, and \(10\) in category C. Two objects are reclassified from B to C.
a) Find the relative frequencies of A, B, and C before and after the change.
b) Explain why the combined relative frequency of B and C does not change.
Hints
- Keep the total fixed while updating the affected category counts.
- Calculate individual shares before and after the reclassification.
- Track the combined count of the two categories as a separate quantity.
Solution
1. Before the change, the relative frequencies are \(\frac{18}{40}=0.45\), \(\frac{12}{40}=0.30\), and \(\frac{10}{40}=0.25\).
2. After the change, the counts are \(18, 10, 12\), so the relative frequencies are \(0.45, 0.25, 0.30\).
3. Before the change, B and C together have relative frequency \(\frac{12+10}{40}=\frac{22}{40}=0.55\).
4. After the change, B and C together still contain the same \(22\) objects, so their combined relative frequency remains \(0.55\).
Answer
Before: A \(0.45\), B \(0.30\), C \(0.25\)
After: A \(0.45\), B \(0.25\), C \(0.30\)
The combined B-and-C relative frequency remains \(0.55\) because objects moved only between those two categories.