7.
a)20%+25%+20%+10%__________30 elevi
100%________________________x elevi
x=(100×30)/75=40 elevi
b)Media=(5+6+7+8+9+10)/6=45/6=7,5
8.
20% este 20/100 sau 1/5
p + p/5 = p' =>p'=6p/5
30% este 30/100 sau 3/10
p' - 3p'/10 = 420 =>7p'/10 = 420 =>p'=600 lei
p=5p'/6 =>p=500 lei
