Question

$\underset{0 \leq i}{\Sigma}\underset{< j}{\Sigma}\underset{< k}{\Sigma}\underset{< \mathcal{l}}{\Sigma}\underset{\leq n}{\Sigma}$ is equal to

• A. ⁿ⁺¹C₄
• B. n .ⁿ⁺¹C₄
• C. ⁿ⁺¹C₃
• D. n(n + 1)

Answer 1

Answer: (B)

n .ⁿ⁺¹C₄

Answer 2

$\underset{0 \leq i}{\Sigma}\underset{< j}{\Sigma}\underset{< k}{\Sigma}\underset{\mathcal{< l}}{\Sigma}\underset{\leq n}{\Sigma}$ n = n $\underset{0 \leq i}{\Sigma}\underset{< j}{\Sigma}\underset{< k}{\Sigma}\underset{< \mathcal{l}}{\Sigma}\underset{\leq n}{\Sigma}$

ß

Selection of 4 terms (from n + 1 terms)

= n. ⁿ⁺¹C₄