The table shows the number of students in four courses across three years. Which year has the highest total enrollment? 
- Step 1: Calculate total for 2011. Sum: $50 + 60 + 40 + 30 = 180$.
- Step 2: Calculate total for 2012. Sum: $55 + 65 + 45 + 35 = 200$.
- Step 3: Calculate total for 2013. Sum: $60 + 70 + 50 + 40 = 220$.
- Step 4: Compare totals. 2013: 220, 2012: 200, 2011: 180. 2013 has the highest enrolment.
- Step 5: Final conclusion. Option (3) 2013 is the correct answer.





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: