13. fie a numarul
2/3×a+ 0,2(6)=40/100⁽²⁰×a
2a/3+ (26-2)90=2/5×a
2a/3+24/90⁽⁶=2a/5
⁵⁾2a/3+4/15=³⁾2a/5
10a+4=6a |-6a
4a+4=0 |-4
4a= -4
a= -1
14. (a+b+c)÷3=15√7
a+b+c= 3×15√7
a+b+c=45√7
(a+b) ÷2=17√7
a+b=2×17√7
a+b=34√7
34√7+c= 45√7 | -34√7
c=11√7
15. fie a numarul
(a+1/3×a) -10=1/2×a
(³⁾a+a/3)-10=a/2
(3a+a)/3-10=a/2
²⁾4a/3 -⁶⁾10=³⁾a/2
8a - 60=3a |-3a
5a -60=0 |+60
5a=60 |÷5
a=12
16. 1/2×(3a-1/5×a)=a+14 |×2
(⁵⁾3a -a/5)=(a+14)×2
(15a-a)/5= 2a+28
14a/5= 2a+28 |×5
14a= 10a+140 | -10a
4a=140 |÷4
a=35
17. fie a suma
a= 2/5×a+19+8
⁵⁾ a=2a/5+⁵⁾27
5a=2a+135 |-2a
3a=135 |÷3
a=45
18. fie a pretul initial
b pretul dupa prima scumpire
a -5%⇒b-5%⇒3610 lei
b -5/100⁽⁵×b=3610
b -1/20×b=3610
²⁰⁾b -b/20=²⁰⁾3610
20b- b=72200
19 b=72200 |÷19
b=3800 lei
a - 5/100⁽⁵×a=3800
a - 1/5×a=3800
⁵⁾a-a/5=⁵⁾3800
5a -a= 19000
4a=19000 |÷4
a= 4750 lei
