∴ The percentages of these four scores are 30%, 40%, 20% and 10% respectively.

∴ The percentage above 80 points is 20%+10% = 30%;

Between 60.5 and 70.5, there are 50 × 30% students = 15 students.

70.5-80.5 students have 50×40%=20 students.

80.5-90.5 students have 50×20%= 10 students.

90.5- 100.5 students have 50× 10%=5 students.

∴ The average score of the participating students is (60.5×15+70.5× 20+80.5×10+90.5× 5) ÷ 50-(70.5× 5+80.5× 20+90.5×).

That is 7 1.5-8 1.5.

The average score of all participating students should be 72 < x < 8 1.