Đáp án:

 

Giải thích các bước giải:

 b8 a) 15 x 2121/4343 + 15 x 222222/434343

= 15x 21/43 + 15 x 22/43 

=15x (21/43 + 22/43)

=15 x 43/43 =15

b) 16x25 + 44x100 / 29x96 +42x48

= 4x100 + 44x100 / 58x48+42x48

= 48x100 / 100x48 =1

c) 1994x1993 - 1992x1993 / 1992x1993 + 1994x7 + 1986

= (1994-1992) x 1993 / 1992x1993 + 1993x7+7+1986

= 2x1993 / 1992x1993 + 1993x7 + 1993

=2x1993 / 1993x8 =2/8 =1/4

b9. a)399x45+55x399 / 1995x1996-1991x1995

= 100x399 / 5x1995

= 100x399 / 5x5x399= 100/25=4

b)1996x1995-996 / 1000+1996x1994

= 1996x1994+1996-996 / 1000+1996x1994

= 1996x1994+1000 / 1000+1996x1994 = 1

c) 637x527 - 189 / 526x637 + 448

= 637x526 + 637-189 / 526x637 + 448

= 637x526 + 448 / 526x637+ 448=1

d)677x874 + 251 / 678x874 - 623

= 677x874 + 251 / 677x874 + 874-623

= 677x874 + 251 / 677x874 + 251=1

lam b8 thoi nha b9 lam phan a, thoi kho lam

8.

a, 15 x 2121/4343 + 15 x 222222/434343

= 15 x 21/43     + 15 x 22/43

= 15 x ( 21/43 + 22/43 )

= 15 x 1

= 15

b, 16 x 25 + 44 x 100/ 29 x 96 + 142 x 48

= 400 + 4 x 11 x 100/ 29 x 96 +71 x 2 x48

= 400 + 400  x  11/29 x 96 + 71 x x 48

= 400 x ( 1+11 ) 96 x (29 + 71 )

= 400 x 12/96 x 100 = 1/2

c, 1994 x 1993 - 1992 x 1993 / 1992 x 1993 + 1994 x 7 + 1986

= 1993 x ( 1994-2 ) / 1992 x 1993 + ( 1993 +1 ) x 7 + 1986

= 1993 x 2 / 1992 x 1993 + 1993 x 7 + 7 + 1986

= 1993 x 2 / 1992 x 1993 + 1993 x 7 + 1993

= 1993 x 2 / 1993 x ( 1992+7+1 )

= 1993x2 / 1993 x 2000 = 2/2000

= 1/1000

9.

a, 399 x 45 + 55 x 399 / 1995 x 1996 - 1991 x 1995

= 399 x ( 45+55 ) / 1995 x ( 1996 - 1991 )

= 399 x 100 / 1995 x 5

= 399 x 20 / 1995

= 399 x 4 / 399

= 4