1a78+4b2+53c=1748+532+abc=2007+abc>abc+2005
dien dau: >
Ta có: 1a78 = 1078 + a x 100 ; 4b2 = 402 x b x 10 ; 53c = 530 + c
Vậy 1a78 + 4b2 + 53c = a x 100 + b x 10 + c + 1078 + 402 + 530 = abc + 2010
Mà abc + 2010 > abc + 2005 suy ra 1a78 + 4b2 + 53c > abc + 2005
Đáp số: 1a78 + 4b2 + 53c > abc + 2005