Bài 1:
a) X x 1999 = 1999 x 199,8
=> X = 199,8
b) (X x 0,25 + 1999 x 2000) = (53 + 1999) x 2000
=> X x 0,25 + 1999 x 2000 = 53 x 2000 + 2000 x 1999
=> X x 0,25 = 53 x 2000
=> X x 0,25 = 106000
=> X = 106000 : 0,25
=> X = 424000
c) 71 + 65 x 4 = (X + 140) : X + 260
=> 71+ 260 = (X + 140) : X + 260
=> (X + 140) : X = 71
=> (X + 140) x 1/X = 71
=> X x 1/X + 1/X x 140 = 71
=> 1 + 1/X x 140 = 71
=> 1/X x 140 = 71 - 1
=> 1/X x 140 = 70
=> 1/X = 70 : 140
=> 1/X = 1/2
=> X = 2
Bài 2:
a) 132 + 77 + 198
= 11 x 12 + 11 x 7 + 11 x 18
= 11 x (12 + 7 + 18)
= 11 x 37
b) 5555 + 6767 + 7878
= 101 x 55 + 101 x 67 + 101 x 78
= 101 x (55 + 67 + 78)
= 101 x 200
c) 1997,1997 + 1998,1998 + 1999,1999
= 1000,1000 x 1997 + 1000,1000 x 1998 + 1000,1000 x 1999
= 1000,1000 x (1997 + 1998 + 1999)
= 1000,1000 x 5994
