70% .... 28 elevi
100% .... x elevi
x = 100*28 / 70 = 40 elevi
elevi care au luat 3 : 40*5/100 = 2
elevi care au luat 4 : 40*5/100 = 2
elevi care au luat 5 : 40*10/100 = 4
elevi care au luat 6 : 40*10/100 = 4
elevi care au luat 7 : 40*15/100 = 6
elevi care au luat 8 : 40*25/100 = 10
elevi care au luat 9 : 40*20/100 = 8
elevi care au luat 10 : 40*10/100 = 4
media pe clasa : 3*2+4*2+5*4+6*4+7*6+8*10+9*8+10*4/40 = 73/40 = 7,3
