a: Sửa đề:\(4,89\cdot4,5+4,89\cdot4,5+4,89\)

\(=4,89\cdot\left(4,5+4,5+1\right)\)

\(=4,89\cdot10=48,9\)

b: \(0,123\cdot7800+1,23\cdot220\)

\(=1,23\cdot780+1,23\cdot220\)

\(=1,23\left(780+220\right)\)

\(=1,23\cdot1000=1230\)

c: \(0,4\cdot0,45\cdot2,5\)

\(=0,4\cdot2,5\cdot0,45\)

\(=1\cdot0,45=0,45\)

d: \(0,2\cdot5,55\cdot50\)

\(=0,2\cdot50\cdot5,55\)

\(=5,55\cdot10=55,5\)

a)\(\frac{{ - 2}}{5} + \frac{3}{7} = \frac{{ - 14}}{{35}} + \frac{{15}}{{35}} = \frac{1}{{35}}\)           

b)\(0,123 - 0,234 =  - \left( {0,234 - 0,123} \right) =  - 0,111.\)

\(0,123.5+0,123:0,25+0,123\)
\(=0,123.5+0.123.4+0,123.1\)
\(=0,123.\left(5+4+1\right)\)
\(=0,123.10=1,23\)
. là dấu nhân.

\(=0,123\times5+0,123\times4+0,123\\ =0,123\left(5+4+1\right)\\ =0,123\times10\\ =1,23\)

\(0,123\) x \(5+0,123:0,25+0,123\)

\(=0,123\) x \(5+0,123\) x \(4+0,123\)

\(=0,123\) x \(\left(5+4+1\right)\)

\(=0,123\) x \(10\)

\(=1,23\)

0,123 x 5 + 0,123 : 0,25 + 0,123       

= 0,123 x 5 + 0,123 x 4 + 0,123       

= 0,123 x ( 5 + 4 + 1 )

= 0,123 x 10

= 1,23

0,123 x 5 + 0,123 x 4 + 0,123

= 0,123 x (5+4+1)

=0,123 x 10

= 1,23

0,123 x 5 + 0,123 x 4 + 0,123

= 0,123 x (5+4+1)

=0,123 x 10

= 1,23

a: x*2,3-4,6=2,3

=>x*2,3=6,9

=>x=3

b: =0,123(5+4+1)

=0,123*10

=1,23

=23,4(54+45+1)

=23,4*100

=2340

D.90,051

D. 90,051
= 3,9

Xu đăng hơn 5 câu mà thế kia;-;

Tội nghịp Xu:>