Total of all 100 numbers = 100 × 50 = 5000.<br><br>
Sum of first 40 = 40 × 45 = 1800.<br>
Sum of next 30 = 30 × 55 = 1650.<br><br>
Sum of final 30 = 5000 − 1800 − 1650 = 1550.<br>
Average of final 30 = 1550 ÷ 30 = 51.666... &asymp; 51.67.<br><br>
Final Answer: 51.67