Đáp án:
$a,37.(25+27)-27.(37+25)$
$=37.25+37.27-27.37-27.25$
$=(37.25-27.25)+(37.27-27.37)$
$=(37-27).25+0$
$=10.25$
$=250$
$b, 5.(13-26)-26.(13-5)+21.13$
$=5.13-5.26-26.13+5.26+21.13$
$=(5.13-26.13+21.13)+(5.26-5.26)$
$=(5-26+21).13+0$
$=0.13+0$
$=0+0$
$=0$