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The problem asks for the number of subsets of set \( A = \{a, b, c, d\} \) that contain exactly 3 elements.

### Solution:
To find the number of such subsets, we use the combination formula:

\[
C(n, r) = \frac{n!}{r!(n-r)!}
\]

Here:
- \( n = 4 \) (the number of elements in set \( A \)),
- \( r = 3 \) (the number of elements in each subset).

Substituting these values:

\[
C(4, 3) = \frac{4!}{3!(4-3)!} = \frac{4 \cdot 3 \cdot 2 \cdot 1}{(3 \cdot 2 \cdot 1)(1)} = 4
\]

Thus, the number of subsets of \( A \) with exactly 3 elements is **4**.

### Explanation:
The subsets of \( A \) containing 3 elements are:
1. \( \{a, b, c\} \),
2. \( \{a, b, d\} \),
3. \( \{a, c, d\} \),
4. \( \{b, c, d\} \).

Let me know if you want further clarification! 

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### Questions for further exploration:
1. What is the total number of subsets of set \( A \)?
2. How many subsets of \( A \) contain exactly 2 elements?
3. How many subsets of \( A \) contain no elements (empty subset)?
4. How does the formula for combinations relate to Pascal's Triangle?
5. Can we generalize this process for larger sets with more elements?

### Tip:
Remember, the sum of the binomial coefficients for a set of \( n \) elements equals \( 2^n \), which represents the total number of subsets of the set!

The number of subset of set A = {a, b, c, d} which has 3 elements is...

Learn how to calculate the number of subsets with exactly 3 elements from the set A = {a, b, c, d}. This combinatorics problem demonstrates the use of the combination formula C(n, r) and is suitable for Grades 8-10.

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