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

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

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

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: 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) 87 x 0,123 + 14 x 0,123 - 0,123

= 87 x 0,123 + 14 x 0,123 - 0,123 x 1

= ( 87 + 14 - 1 ) x 0,123

= 100 x 0,123

= 12,3

b) 25 x 12,5 x 0,4 x 0,8

= ( 25 x 0,4 ) x ( 12,5 x 8 )

= 10 x 100

= 1000

c) 23 + 26 + 29 + .... + 56

Khoảng cách cách đều là 3.

Số số hạng là : ( 56 - 23 ) : 3 + 1 = 12 ( số )

Tổng là : ( 56 + 23 ) x 12 : 2 = 474

a, 0,123 x (87+14-1)

=0,123 x 100

=12,3

b, (25x0,4)x(12,5x0,8)

=10x10

100

\(0,875-0,15+0,25-0,85-0,125+0,6+0,4+0,123\)

\(=\left(0,875-0,125+0,25\right)-\left(0,85+0,15\right)+\left(0,6+0,4\right)+0,123\)

\(=1-1+1+0,123\)

\(=1+0,123=1,123\)

a: \(0,123\cdot450+1,23\cdot55\)

\(=1,23\cdot45+1,23\cdot55\)

\(=1,23\left(45+55\right)=1,23\cdot100=123\)

b: \(0,234\cdot3700+23,4\cdot62\cdot26\cdot9\)

\(=23,4\cdot37+23,4\cdot62\cdot26\cdot9\)

\(=23,4\left(37+62\cdot26\cdot9\right)=340353\)

a, 2,35 x 10 = 23,5

b, 0,123 x 10 = 1,23

c, 4,07 x 100 =  407

d, 0,205 x 100 = 20,5

e, 3,18 x 1000 = 3180

f, 0,376 x 1 000 = 376

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

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