Răspuns :
Ma = 420 = > S = 3 x Ma = 3 x 420 = 1260
Fie a, b, c numerele cautate cu proprietatea :
b = a + 1
c = a + 2
a + b + c = 1260
a + a + 1 + a + 2 = 1260
3a = 1257
a = 1257 : 3
a = 419
b = 420
c = 421
( a + a + 1 + a + 2 ) : 3 = 420
( 3 × a + 1 + 2 ) : 3 = 420
3 × a + 1 + 2 = 420 × 3
3 × a + 1 + 2 = 1260
3 × a + 1 = 1260 - 2
3 × a + 1 = 1258
3 × a = 1258 - 1
3 × a = 1257
a = 1257 : 3
a = 419
a + 1 = 419 + 1 = 420
a + 2 = 419 + 2 = 421
( 3 × a + 1 + 2 ) : 3 = 420
3 × a + 1 + 2 = 420 × 3
3 × a + 1 + 2 = 1260
3 × a + 1 = 1260 - 2
3 × a + 1 = 1258
3 × a = 1258 - 1
3 × a = 1257
a = 1257 : 3
a = 419
a + 1 = 419 + 1 = 420
a + 2 = 419 + 2 = 421
