Suppose *** 100 people.

X0+...+X5 = 100。

0 * x0+x 1+2 * x2+3 * x3+4 * x4+5 * X5 = 80+95+85+79+74；

3(x3+x4+X5)+x 1+2 * x2+x4+2 * X5 = 4 13

3(x3+x4+X5)= 4 13-(x 1+2 * x2+x4+2 * X5)

= 4 13-( 100-x0-x3-x4-X5+x4+2 * X5+x2)

=3 13-(x5-x0-x3+x2)

(x0+x3)+(x2+X5)& lt； = 100

get

3(x3+x4+X5)》= 3 13-( 100-2(x0+x2))》= 2 13

At least 7 1. 1