递等式计算．（能简便运算的要用简便方法运算．）①239.8-19.8÷0.4×2.5②8.3×6.2+0.83×39-8.3×0.1③7.14+3.95+（2.86-1.95）④1.5×[（4.8-0.48÷0.6）+2.6]．

Question

递等式计算．（能简便运算的要用简便方法运算．）
①239.8-19.8÷0.4×2.5            
②8.3×6.2+0.83×39-8.3×0.1
③7.14+3.95+（2.86-1.95）
④1.5×[（4.8-0.48÷0.6）+2.6]．

Answer 1

①239.8-19.8÷0.4×2.5   
=239.8-49.5×2.5
=239.8-123.75
=116.05；
②8.3×6.2+0.83×39-8.3×0.1
=8.3×（6.2+3.9-0.1）
=8.3×10
=83；
③7.14+3.95+（2.86-1.95）
=（7.14+2.86）+（3.95-1.95）
=10+2
=12；
④1.5×[（4.8-0.48÷0.6）+2.6]
=1.5×[（4.8-0.8）+2.6]
=1.5×[4+2.6]
=1.5×6.6
=9.9．