用一个简单的方法计算以下问题:2.5×101-2.5 0.25×12.7×4 27.25-(4.34+7.25)21.9-14.9-5。

=2.5×100+2.5-2.5,

=250;

(2)0.25×12.7×4

=0.25×4×12.7,

=1×12.7,

=12.7;

(3)27.25-(4.34+7.25)

=27.25-7.25-4.34,

=20-4.34,

=15.66;

(4)21.9-14.9-5.1

=21.9-(14.9+5.1),

=21.9-20,

=1.9;

(5)7.4+3.9+12.6

=(7.4+12.6)+3.9,

=20+3.9,

=23.9;

(6)2.5×2.4

=2.5×4×0.6,

=10×0.6,

=6.