1.
a+b+c=99
0,5=1/2
0,8=4/5
a/2=2b=5c/4=k
a=2k
b=k/2
c=4k/5
2k + k/2 + 4k/5 = 99
20k+5k+8k=990
33k=990 =>k=30
=>a=60
=>b=15
=>c=24
2.
a)25% este 25/100=1/4
1/4 · 256 = 64
b)15% este 15/100=3/20
3x/20=6 =>3x=120 =>x=40
c)119 _______ 100%
17 _______ x
x=1700/119=14,285...%