Total of all 60 items = 60 × 30 = 1800.<br><br>
Group 1 total = 25 × 24 = 600.<br>
Group 2 total = 15 × 36 = 540.<br><br>
Group 3 has 60 − 25 − 15 = 20 items.<br>
Group 3 total = 1800 − 600 − 540 = 660.<br>
Group 3 average = 660 ÷ 20 = 33.<br><br>
Final Answer: 33