If `A = {1,2,3,4,5,6,7,8,9,10}` and `B = {2,4,6,8,10}`, then `n(A-B)` is ______

Answer

To solve the problem, we need to find the number of elements in the set difference \( A - B \), where:

- \( A = \{1, 2, 3, 4, 5, 6, 7, 8, 9, 10\} \)
- \( B = \{2, 4, 6, 8, 10\} \)

### Step-by-Step Solution:

1. **Identify the Elements of Set A**:
- The set \( A \) contains the elements: \( 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 \).

2. **Identify the Elements of Set B**:
- The set \( B \) contains the elements: \( 2, 4, 6, 8, 10 \).

3. **Find the Set Difference \( A - B \)**:
- The set difference \( A - B \) consists of elements that are in \( A \) but not in \( B \).
- We will remove all elements of \( B \) from \( A \):
- Start with \( A \): \( 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 \)
- Remove \( 2 \): Remaining elements are \( 1, 3, 4, 5, 6, 7, 8, 9, 10 \)
- Remove \( 4 \): Remaining elements are \( 1, 3, 5, 6, 7, 8, 9, 10 \)
- Remove \( 6 \): Remaining elements are \( 1, 3, 5, 7, 8, 9, 10 \)
- Remove \( 8 \): Remaining elements are \( 1, 3, 5, 7, 9, 10 \)
- Remove \( 10 \): Remaining elements are \( 1, 3, 5, 7, 9 \)

4. **List the Remaining Elements**:
- After removing all elements of \( B \) from \( A \), the remaining elements are \( 1, 3, 5, 7, 9 \).

5. **Count the Number of Elements in \( A - B \)**:
- The remaining elements are \( 1, 3, 5, 7, 9 \).
- Count these elements: There are 5 elements.

### Final Answer:
The number of elements in \( A - B \) is \( 5 \).

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