a) \(2,23\cdot0,1+3,34:10+1:10\cdot4,43\)

\(=2,23\cdot0,1+3,34\cdot0,1+4,43\cdot0,1\)

\(=0,1\cdot\left(2,23+3,34+4,43\right)\)

\(=1\)

b) \(4,5:100+5,4\cdot0,01+1:100\cdot0,1\)

\(=4,5\cdot0,01+5,4\cdot0,01+0,1\cdot0,01\)

\(=0,01\left(4,5+5,4+0,1\right)\)

\(=0,1\)

b: =(4,5+5,4)x0,01

=9,9x0,01

=0,099

a)432

b)0,5075

c)0,356

d)1

a) 43,2 x 10 = 432

b) 5,078 : 10 = 0,5078

c) 3,56 x 0,1 = 0,356

d) 0,1 x 10 = 1

A=28,875                                                        B=327,6

1) 10 000

2) 16 000

3) 1,2

4) 0.1

5) 460

6) 48

7) 240

          ~ Chúc bạn học tốt <3

10 x 1000 = 10000

1600 x 10 = 16000

12 x 0,1 = 01,2

10 x 0,01= 0,10 

46 : 0,1 = 4,6

24 : 0,5 = 48

60 : 0,25 = 24

~~ chưa chắc đã đúng ~~

hok tốt 

Tính nhẩm:

a) 78,29 x 10

78,29 x 0,1

b) 265,307 x 100

265,307 x 0,01

c) 0,68 x 10

0,68 x 0,1

Tính nhẩm:

a) 78,29 x 10=782,9

78,29 x 0,1=7,829

b) 265,307 x 100=26530,7

265,307 x 0,01=2,65307

c) 0,68 x 10=6,8

0,68 x 0,1=o,068

1, Số học sinh lớp 5A là :   
        800 : 100 x 5 = 40 ( học sinh )
     Số bạn nữ lớp 5A là
        40 : 100 x 40 = 16 ( học sinh )
                                

a) \(\frac{1}{2}\times x-3=6\)

=> \(\frac{1}{2}\times x=6+3\)

=> \(\frac{1}{2}\times x=9\)

=>\(x=9:\frac{1}{2}\)

=> \(x=18\)

b) \(2:x=\frac{2}{5}--\frac{1}{10}\)

=> \(2:x=\frac{2}{5}+\frac{1}{10}\)

=> \(2:x=\frac{1}{2}\)

=> \(x=2:\frac{1}{2}\)

=> \(x=4\)

c) \(25-\left(2\frac{1}{2}+x\right)=10\)

=> \(2\frac{1}{2}+x=25-10\)

=> \(\frac{5}{2}+x=15\)

=>\(x=15-\frac{5}{2}\)

=> \(x=\frac{25}{2}\)

d) \(\left(x-\frac{3}{4}\right)\times3-45:9=10\)

=> \(\left(x-\frac{3}{4}\right)\times3-5=10\)

=> \(\left(x-\frac{3}{4}\right)\times3=10+5\)

=> \(\left(x-\frac{3}{4}\right)\times3=15\)

=> \(\left(x-\frac{3}{4}\right)=15:3\)

=> \(\left(x-\frac{3}{4}\right)=5\)

=> \(x=5+\frac{3}{4}\)

=> \(x=\frac{23}{4}\)

\(a,\frac{1}{2}.x-3=6\Rightarrow\frac{x}{2}=9\Rightarrow x=18\)

\(b,2:x=\frac{2}{5}-\frac{1}{10}\Rightarrow\frac{2}{x}=\frac{9}{10}\Rightarrow x=\frac{2.10}{9}=\frac{20}{9}\)

\(c,25-\left(2\frac{1}{2}+x\right)=10\Rightarrow25-\frac{5}{2}+x=10\Rightarrow x=10+\frac{5}{2}-25=-\frac{25}{2}\)

\(d,\left(x-\frac{3}{4}\right).3-45:9=10\Rightarrow\left(x-\frac{3}{4}\right).3-5=10\Rightarrow\left(x-\frac{3}{4}\right).3=15\Rightarrow x-\frac{3}{4}=5\Rightarrow x=\frac{23}{4}\)

\(\Leftrightarrow10\times\left(\frac{1}{1\times2}+\frac{1}{2\times3}+...+\frac{1}{x\times\left(x+1\right)}\right)=9\)

\(\Leftrightarrow\left(\frac{1}{1}-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+...+\frac{1}{x}-\frac{1}{x+1}\right)=9\div10\)

\(\Leftrightarrow\frac{1}{1}-\frac{1}{x+1}=\frac{9}{10}\)

\(\Leftrightarrow\frac{1}{x+1}=1-\frac{9}{10}\)

\(\Leftrightarrow\frac{1}{x+1}=\frac{1}{10}\)

\(\Rightarrow x+1=10\)

\(\Leftrightarrow x=9\)

Vậy x = 9