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a+b = 60
a-b=20

a=?
b=?


Răspuns :

40+20=60

40-20=20

a=40
b=20
a+b= 60
a-b=20 
a=20+b
20+b+b=60
20+2b=60
2b=60-20
2b=40
b=40:2
b=20
a= 20+20 = 40