p 1 = 8%
p 2= 12%
p 3= 15%
M = 40%
78 elevi nu au primit nimic
40%+15%+12%+8%=75%
100%-75% = 25% din elevi nu au primit nimic
a) 25% = 78 elevi
50%= 78+78= 156 elevi
100%= 156+156= 312 elevi au participat la olimpiada
b) 25%+25%= 50%=> 78+78= 156
50%-40% = 10% => 156- 20= 136 de elevi au luat mentiune (40%)