Gọi số thứ 1 là b ; 2 là b ; 3 là c
=>a = 2b + 1 (1)
b= 3c + 5 (2)
Thay (2) vào (1) => a = 2(3c+5) + 1 = 6c + 11
=> a + b + c =1256 = 6c + 11 + 3c + 5 + c = 10c + 16
=> 10c = 1240
=>c=124
=>b = 3c + 5 = 377
=> a = 1256 - 124 - 377 = 755
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