1. a)81+243+19 b)268+89+232+11 c)5 . 25 . 2 . 33 . 4
=81+19+243 =(268+232)+(89+11) =(5 . 2) . (25 . 4) . 33
=100+243 =500+100 =10 . 100 . 33
=343 =600 =3 000
d)53 . 52+48 . 53 e)31+32+33+......+39
=53 . (52+48) =(31+39)+(32+38)+(33+37)+(34+36)+35
=53 . 100 =70x4+35
=5 300 =280+35
=315
g)23 . (133+67)+(67+133) . 77
=23 . 200+200 . 77
=200 . (23+77)
=200 . 100
=20 000
3.a)(X-6) . 25=0 b)27 . (x-35)=27 c)207+(x+35)=312
X-6=0 . 25 x-35=27:27 x+35=312-207
X-6=0 x-35=1 x+35=105
X =0+6 x =1+35 x =105-35
X =6 x =36 x =70
Xong rồi nha! Chúc học giỏi!
