a)notam elevi =E fete =F baieti=B
E=25
F=40%
25=100% din numarul E
folosim regula de trei simpla
25(E).....................100%
?(F)........................40%
F=(40x25):100
F=10
b)
B=25(E)-10(F)
B=15
10=100%din numarul F
10(F)...............100%
15(B)................?%
?=(15x100):10=150
15(B)=150% din numarul F
c)
varianta cea mai simpla :
stim ca F reprezinta 40%
atunci B=100%-40%
B=60%
d)25(E)+3(B)=28(E)
28(E).................100%
10(F)..................?%
?=(10x100):28
?=1000:28=250:7
?=35.7143% din nr E
