Răspuns:
Explicație pas cu pas:
1.
f+b=30
b=2f/3 2f/3+f=30 2f+3f=90 5f=90 f=18
b=2·18/3=2·6=12
fete=18
baieti=12
2.
a+b=2·24
a/b=5/7 a=5b/t 5b/7+b=48 5b+7b=7·48 12b=7·48
b=28
a=5·28/7=20
3.
x-y=10
x/4=2y/5-2 (y+10)/4=2y/5-2 5y+50=8y-40 3y=90
y=30
x=40 verif 40:4=2·30/5-2 10=12-2