a + b = 35
b + c = 65
a + c = 60
__________________ → adun sumele
2 x a + 2 x b + 2 x c = 35 + 65 + 60
2 x ( a + b + c ) = 160
a + b + c = 160 : 2
a + b + c = 80 → suma celor trei numere
______________________________
80 - 65 = 15 ( a )
35 - 15 = 20 ( b )
65 - 20 = 45 ( c )
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a + b = 15 + 20 = 35
b + c = 20 + 45 = 65
a + c = 15 + 45 = 60
