2.7-a-b=2.7-(+)
6.1×m×n=6.1×(×)
34×x+3.4×y=×(+)
8.52﹣(5.52+0.9)
4×(9.3﹣5.7)+3.6
7.5×101
(0.38+0.38+0.38+0.38)×2.5