a, 72,9 x 99 + 72 + 0,9

= 72,9 x 99 + 72,9

= 72,9 x 99 + 72,9 x 1 

= 72,9 x ( 99 + 1 )

= 72,9 x 100

= 7290

b, 0,8 x 96 + 1,6 x 2

= 0,8 x 96 + 0,8 x 2 x 2 

= 0,8 x ( 96 + 2 + 2 ) 

= 0,8 x 100

= 80

\(12371-5428+1429=\left(12371+1429\right)-5428=13800-5428=8372\\ 36,44\times99+36+0,4=36,4\times\left(100-1\right)+\left(36+0,4\right)=36,4\times100-36,4+36,4=3640+0=3640\)

12371 - 5428 + 1429

= {12371 + 1429} - 5428

=  13800 - 5428

=8,372

36,4 * 99 + 36 + 0,4

= 36,4 * 99 + 36,4

= 36,4 * [ 99 + 1 ]

= 36,4 * 100

= 3640

lưu ý đấu * là nhân nhé

a) 4 x 78 x 5

= (4 x 5) x 78

= 20 x 78

= 1560

b) 2 x 99 x 5

= (2 x 5) x 99

= 10 x 99

= 990

Cảm ơn bạn.

\(99\times36+57\times99+99-84\times99\)

\(=99\times(36+57+1-84)\)

\(=99\times10=990\)

99 x 36 + 57 x 99 - 84 x 99

= 99 x ( 36 + 57 + 1 - 84 )

= 99 x 10

= 990

3640

3640

99 x 15 + 15 = 15 x ( 99 + 1) = 15 x 100 = 1500

7,48 x ( 99 + 1 )

= 7,48 x 100

= 748

7,48 x ( 99 + 1 )

= 7,48 x 100

= 748

sorry =79,9x100=7990

79,9x99+79,9=79,9x(99+1)=79,9x10=799

Hướng dẫn giải:

a) 4 x 78 x 5 = (4 x 5) x 78 = 20 x 78 = 1560

b) 2 x 99 x 5 = (2 x 5) x 99 = 10 x 99 = 990

c) 6 x 31 x 5 = (6 x 5) x 31 = 30 x 31 = 930

d) 8 x 63 x 5 = (8 x 5) x 63 = 40 x 63 = 2520

\(=0,15\times\left(99+2-1\right)=0,15\times100=15\)