a + b = 31
b- 7 =a:3 ⇒ 3 × (b-7) = a⇒3b - 21 = a
(3b - 21) + b = 31
4b = 31 + 21⇒4b = 52⇒b = 13
a = 31 - b = 18 deci a = 18 si b = 13
2.
a + b + c + d = 36
(a +b ) = ( c + d ):2
2a + 2b = c + d dar a + b + c + d = 36
a + b + 2a + 2b =36
3a + 3b = 36⇒ a + b =12
si c + d = 2× (a + b) = 24
a + b = 12 , a si b consecutive impare
deci a + (a +2)= 12⇒ 2a = 12 - 2⇒ a = 10 :2⇒ a =5
iar b = a + 2 =5 + 2 = 7 deci a = 5 si b = 7
c + d =24
iar c si d consecutive impare
c +(c +2) =24
2c =22
c = 11 iar d = c + 2 = 13 deci a = 5; b = 7; c = 11 si d = 13
a+b=31
b-7=a:3/x3
3b-21=a
a=3b-21
3b-21+b=31
2b=31-21
2b=10
b=10:2
b=5
