ex 1) 3x/7=carti in lb romana
x-3x/7=4x/7 = rest
4x/7 × 5/9=20x/63=carti in lb engleza
3x/7+20x/63+320=x
27x+20x+20160=63x
16x=20160
x=1260 carti
1260×3/7=540carti in lb romana
1260-540=720
720×5/9=400carti in lb engleza
720-400=320carti in lb franceza
ex 2 A=L•2L/3=96 cm^2
2L^2=96 cm^2•3
2L^2=288 cm^2
L^2=144 cm^2
L=12 cm
l=2•12/3cm =8 cm
Lungimea 12cm
Lătimea 8 cm. Perimetrul = 12cm•2+8cm•2=40 cm ex 3. a*3=a+4/5
15a=5a+4
15a-5a=4
10a=4
a=4/10
a=2/5
ex 4) m=(a+b)/2
24=(a+b)/2
a+b=48 dar mai stim ca a=3b/5
3b/5+b=48
3b/5+5b/5=48
8b/5=48
b=30
a=48-b
a=48-30=18
ex 5) a+b+c /3 =120 ; a+b+c =120*3 ; a+b+c =360
a =2b/3
a =c-80 ; c =a+80 ;c =2b/3 +80
2b/3 + b + 2b/3+80 = 360 numitor 3
2b +3b +2b +240 =1080
7b =1080-240
7b =840
b =120
a =2b/3
a =2*120/3 =240/3 =80
c =a+80
c =80+80 =160
verif ; 80+120+160/3 =360/3 =120
ex 6) prima zi avem 3/8 din x
a doua zi avem 2/5din x-3/8x
adica 2/8 din x
a treia zi 180 kg
deci 3/8x+2/8x+180=x
5x-8x+1440=0
3x=1440
x=480 sper ca sunt corecte.
