用简便方法计算.6.2+5.18+2.8 15.35-(5.35+7.2) 3.63-1.25+17.37-8.75 13.7-9.9 98×45+2×45 56×102.
(1)6.2+5.18+2.8, =6.2+2.8+5.18, =9+5.18, =14.18; (2)15.35-(5.35+7.2), =15.35-5.34-7.2, =10-7.2, =2.8; (3)3.63-1.25+17.37-8.75, =(3.63+17.37)-(1.25+8.75), =21-10, =11; (4)13.7-9.9, =13.7-10+0.1, =3.7+0.1, =3.8; (5)98×45+2×45, =45×(98+2), =45×100, =4500; (6)56×102, =56×100+56×2, =5600+112, =5712. |