Explanation: 
Another Explanation (5):
bài toán: nC5 = nC7 হলে, nC9 এর মান কত? 🤔
আমরা জানি, nCr = nCn-r 🤩
তাহলে, nC5 = nC7 থেকে পাই,
n = 5 + 7 = 12 🥳
অতএব, nC9 = 12C9 = 12C(12-9) = 12C3 🥰
এখন, 12C3 = \(\frac{12!}{3!(12-3)!}\) = \(\frac{12!}{3!9!}\) = \(\frac{12 \times 11 \times 10}{3 \times 2 \times 1}\) = 2 \times 11 \times 10 = 220 😎
সুতরাং, nC9 = 220 🤓