x-numarul total de bile
30% din x=30/100×x=3x/10-bile albe
20% din 3x/10=20/10×3x/10=1/5×3x/10=3x/50-bile rosii
3x/10+3x/50+32=x aducem la acelasi numitor
15x+3x+1600=50x
18x-50x=-1600
-32x=-1600
32x=1600
x=50bile
a) 3×50/10=3×5=15-bile albe
3×50/50=3-bile rosii
b) probabilitatea=numarul cazurilor favorabile/numarul cazurilor posibile
p=32/50=16/25
c) p% din 15=3
p/100×15=3
p/100=3/15
p/100=1/5
p=100/5=20%