6.3÷4.2
=(6.3÷2.1)÷(4.2÷2.1)
=3÷2
=1.5
999×99+199
=(999×99+99)+100
=(999+1)×99+100
=1000×99+100
=99000+100
=99100
递等式计算(能简算要简算）,6.3除以4.2.999乘99加199
6.3÷4.2
=(6.3÷2.1)÷(4.2÷2.1)
=3÷2
=1.5
999×99+199
=(999×99+99)+100
=(999+1)×99+100
=1000×99+100
=99000+100
=99100