Ma =(a+b+c+d):4 = 33
a+b+c+d = 33×4 = 132
b = a+18
c = 2a
d = (a+b):2
inlocuim pe b cu a+18
d = (a+a+18):2
d =( 2a+18):2 = 2×(a+9):2 = a+9
inlocuim in a 2-a ecuatie
a+a+18+2a+a+9 = 132
5a+27 = 132
5a = 132-27
5a = 105 |:5
a = 21
b = 21+18 = 39
c = 2×21 = 42
d = 21+9 = 30
Verificare:
(21+39+42+30):4 = 132:4 = 33
a = 21
b = 39
c = 42
d = 30