a+b b+a
ax(bxc) (axb)xc
axc+bxc (a+b)xc
2.
41+216+159
=(41+159)+216
=200+216
=416
45x16
=45x2x8
=90x8
=720
12x13x5
=12x5x13
=60x13
=780
230-76-124
=230-(76+124)
=230-200
=30
19+99x19
=19x(1+99)
=19x100
=1900
256x9-56x9
=(256-56)x9
=200x9
=1800
3.
116 18900 69
4.
(1)
0 123
1 1234
12 12345
(本网页感谢网友qq为3126396745纠错)