a, \(\overline{a,87}\) + \(\overline{2,b2}\)
= \(\overline{a,0}\) + 0,87 + 2,02 + \(\overline{0,b}\)
= \(\overline{a,b}\) + 2,89
vì 2,89 > 2,86 vậy \(\overline{a,87}\) + \(\overline{2,b2}\) > \(\overline{a,b}\) + 2,86
b, \(\overline{a,bc}\) + 20,04+ 28,63
= \(\overline{a,bc}\) + 48,67
= 48,67 + \(\overline{a,b}\) + \(\overline{0,0c}\)
=\(\overline{48,67c}\) + \(\overline{a,b}\)
\(\overline{3a,81}\) + \(\overline{4,b5}\) + 13,9
= 30,81 + \(\overline{a,0}\) + 4,05 + 13,9 + \(\overline{0,b}\)
= 48,76 + \(\overline{a,b}\)
Vì 48,76 > \(\overline{48,67c}\)
Nên \(\overline{3a,81}\) + \(\overline{4,b5}\) + 13,9 > \(\overline{a,bc}\) + 20,04 + 28,63