递等式。。是四则运算(눈_눈)7×99＝7×（100-1）＝700-7＝693
7x99=7x(100一1) =7x100一7x1 =700一7 =693
4.9✖️0.37➗0.37✖️4.9用简便方法计算4.9✖️0.37➗0.37✖️4.9=4.9*4.9*0.37÷0.37=24.01*1=24.01
