a)
a/3=b/4
b/6=c/5
4a=3b sau 12a=9b
5b=6c sau 10b=12c
a/9=b/x
x=9b/a=12a/a=12
x=12
b/12=c/y
y=12c/b=10b/b=10
y=10
b)
Aplicam regula de 3 simpla:
12...........100%
9................x%
x%=9*100/12=75
x%=75
c)
Sistem de 3 ec. cu 3 nec.:
3a-2b+c=26
4a=3b, a=3b/4
5b=6c, c=5b/6
3(3b/4)-2b+5b/6=26
9b/4-2b+5b/6=26
27b-24b+10b=312
13b=312
b=24
a=3*24/4=18
a=18
c=5*24/6
c=20