2.
a)800_________ 100%
20_________ x
x=2000/800=20/8=2,5%
b)50__________ 100%
4__________ x
x=400/50=8%
c)400__________ 100%
28__________ x
x=2800/400=7%
d)54___________ 100%
12___________ x
x=1200/54=200/9=22,(2)%
e)2,5___________ 100%
0,5___________ x
x=50/2,5=500/25=20%
4.
a+b=3900
12% este 12/100=3/25
8% este 8/100=2/25
3a/25=2b/25-12
3a=2b-300 =>a=(2b-300)/3
(2b-300)/3 + b = 3900
2b-300+3b=11700
5b=11700+300
5b=12000 =>b=2400 si a=1500
