In how many ways can 5 identical balls be distributed into 3 distinct boxes?
35
- Step 1: Recognizing the problem type - This is a "stars and bars" problem (distributing identical objects into distinct boxes).
- Step 2: Formula - Number of non-negative integer solutions to: \[ x_1 + x_2 + x_3 = 5 \] is: \[ \binom{n+k-1}{k-1} = \binom{5+3-1}{3-1} = \binom{7}{2} \]
- Step 3: Calculating - \[ \binom{7}{2} = \frac{7 \times 6}{2 \times 1} = 21 \]
- Step 4: Conclusion - There are 21 ways, matching option (2).
For any natural number $k$, let $a_k = 3^k$. The smallest natural number $m$ for which \[ (a_1)^1 \times (a_2)^2 \times \dots \times (a_{20})^{20} \;<\; a_{21} \times a_{22} \times \dots \times a_{20+m} \] is: