例1 98×12=(100-2) ×12=1 200-24=1 176;
例2 -16×233+17×233=(-16+17)×233=233.
请你参考黑板中老师的讲解,用运算律简便计算:
小军:原式 =(49 + )×(–5)= 49×(–5)+ ×(–5)
=–245–4 =–249 ;
小明:原式 = – × 5 = – = – 249 ;
小丽:原式 =(49 + )×(-5)=(50 -1 + )×(-5)
=(50 - )×(-5)= 50 ×(-5)+( - ) ×(-5)
= –250 + = –249 ;
19 ×(– 8)