Combination Multiplier
1. **State the problem:** Calculate the value of $\binom{400}{2} \times 500$.
2. **Recall the formula for combinations:**
$$\binom{n}{k} = \frac{n!}{k!(n-k)!}$$
This formula gives the number of ways to choose $k$ items from $n$ without regard to order.
3. **Apply the formula for $\binom{400}{2}$:**
$$\binom{400}{2} = \frac{400!}{2!(400-2)!} = \frac{400 \times 399}{2 \times 1}$$
We simplify factorials by canceling terms.
4. **Calculate $\binom{400}{2}$:**
$$\binom{400}{2} = \frac{400 \times 399}{2} = 200 \times 399 = 79800$$
5. **Multiply by 500:**
$$79800 \times 500 = 39900000$$
6. **Final answer:**
$$\binom{400}{2} \times 500 = 39900000$$
This means there are 39,900,000 ways when combining the selection and multiplication as described.