\(\dfrac{8}{15}\times\dfrac{11}{2}+\dfrac{7}{15}\times\dfrac{11}{2}=\dfrac{11}{2}\left(\dfrac{8}{15}+\dfrac{7}{15}\right)=\dfrac{11}{2}\times\dfrac{15}{15}=\dfrac{11}{2}\times1=\dfrac{11}{2}\)

\(\dfrac{8}{12}+\dfrac{30}{12}-\dfrac{9}{12}=\dfrac{19}{12}\)

\(\dfrac{24}{30}-\dfrac{15}{30}+\dfrac{10}{30}=\dfrac{19}{30}\)

`8 / 15 : 2 / 11 + 7 / 15 : 2 / 11`

`= ( 8 / 15 + 7 / 15 ) : 2 / 11`

`= 15 / 15 xx 11 / 2`

`= 1 xx 11 / 2 = 11 / 2`

_________________________________

`2 / 3 + 5 / 2 - 3 / 4`

`= 8 / 12 + 30 / 12 - 9 / 12`

`= 29 / 12`

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`4 / 5 - 1 / 2 + 1 / 3`

`= 24 / 30 - 15 / 30 + 10 / 30`

`= 19 / 30`

Ta có: \(B=\frac{1}{46}+\frac{2}{45}+\cdots+\frac{44}{3}+45\)

\(=\left(\frac{1}{46}+1\right)+\left(\frac{2}{45}+1\right)+\cdots+\left(\frac{44}{3}+1\right)+1\)

\(=\frac{47}{46}+\frac{47}{45}+\cdots+\frac{47}{3}+\frac{47}{47}=47\left(\frac13+\frac14+\cdots+\frac{1}{47}\right)\) =47A

=>\(\frac{A}{B}=\frac{1}{47}\)

1: 243^5=(3^5)^5=3^25

3*27^8=3*(3^3)^8=3^25

=>243^5=3*27^8

6: 125^5=(5^3)^5=5^15

25^7=(5^2)^7=5^14

=>125^5>25^7(15>14)

5: 78^12-78^11=78^11(78-1)=78^11*77

78^11-78^10=78^10*77

mà 11>10

nên 78^12-78^11>78^11-78^10

Sửa đề: \(\left(\frac{1}{1\cdot2\cdot3}+\frac{1}{2\cdot3\cdot4}+\cdots+\frac{1}{8\cdot9\cdot10}\right)\cdot x=\frac{44}{45}\)

Đặt \(A=\frac{1}{1\cdot2\cdot3}+\frac{1}{2\cdot3\cdot4}+\cdots+\frac{1}{8\cdot9\cdot10}\)

\(=\frac12\left(\frac{2}{1\cdot2\cdot3}+\frac{2}{2\cdot3\cdot4}+\cdots+\frac{2}{8\cdot9\cdot10}\right)\)

\(=\frac12\left(\frac{1}{1\cdot2}-\frac{1}{2\cdot3}+\frac{1}{2\cdot3}-\frac{1}{3\cdot4}+\cdots+\frac{1}{8\cdot9}-\frac{1}{9\cdot10}\right)\)

\(=\frac12\left(\frac12-\frac{1}{90}\right)=\frac12\cdot\frac{44}{90}=\frac{22}{90}=\frac{11}{45}\)

Ta có: \(\left(\frac{1}{1\cdot2\cdot3}+\frac{1}{2\cdot3\cdot4}+\cdots+\frac{1}{8\cdot9\cdot10}\right)\cdot x=\frac{44}{45}\)

=>\(x\cdot\frac{11}{45}=\frac{44}{45}\)

=>\(x=\frac{44}{45}:\frac{11}{45}=\frac{44}{11}=4\)

\(=5+\dfrac{2}{5}+4+\dfrac{3}{7}-\dfrac{1}{4}+\dfrac{4}{7}-2-\dfrac{2}{5}-\dfrac{3}{4}\)

\(=\left(5+4-2\right)+\left(\dfrac{2}{5}-\dfrac{2}{5}\right)+\left(\dfrac{3}{7}+\dfrac{4}{7}\right)-\dfrac{1}{4}-\dfrac{3}{4}\)

=7+1-1

=7

`#lv`

`5 2/5 + 4 3/7 - 1/4 + 44/77 - 2 2/5 - 0,75`

`= 27/5 + 31/7 - 4/7 - 12/5 - 3/4`

`= (27/5 - 12/5) + (31/7 - 4/7) + ( 1/4 + 3/4)`

`= 3 + 27/7 + 1`

`= 4 + 27/7`

`= 28/7 + 27/7`

`= 56/7`

`= 8`

= 492309

thông cảm nha, mk chỉ vít đc như zậy thui, diễn giải ra dài dòng lắm

492309

ý mình là 38 phần 3 trừ trong ngoặc 29 phần 5 trừ 10 phần 3 cộng 39 phần 5 trong ngoặc phần 44 phần 5 trừ trong ngoặc 2 phần 3 cộng 27 phần 5 trong ngoặc trừ 1 phần 3

1+2+3+4+5+6+7+8+9+1+2+3+4+5+6+7+8+9+0+0+0+3+4+1+2+3+111+44+99 = 357

1+2+3+4+5+6+7+8+9+1+2+3+4+5+6+7+8+9+0+0+0+3+4+1+2+3+111+44+99=357