a, \(\dfrac{27}{45}+\dfrac{12}{30}=\dfrac{3}{5}+\dfrac{2}{5}=\dfrac{5}{5}=1\)

b, \(\dfrac{6}{18}+\dfrac{1}{3}=\dfrac{1}{3}+\dfrac{1}{3}=\dfrac{2}{3}\)

a) 27/45 + 12/30

= 3/5 + 2/5

= 5/5 =1.

b) 6/18 + 1/3

=1/3 + 1/3

= 2/3.

\(3\cdot\left(3x-\dfrac{1}{2}\right)^3+\dfrac{1}{9}=0\)

\(\Rightarrow3\cdot\left(3x-\dfrac{1}{2}\right)^3=-\dfrac{1}{9}\)

\(\Rightarrow\left(3x-\dfrac{1}{2}\right)^3=-\dfrac{1}{9}:3\)

\(\Rightarrow \left(3x-\dfrac{1}{2}\right)^3=-\dfrac{1}{27}\)

\(\Rightarrow\left(3x-\dfrac{1}{2}\right)^3=\left(-\dfrac{1}{3}\right)^3\)

\(\Rightarrow3x-\dfrac{1}{2}=-\dfrac{1}{3}\)

\(\Rightarrow3x=-\dfrac{1}{3}+\dfrac{1}{2}\)

\(\Rightarrow3x=\dfrac{1}{6}\)

\(\Rightarrow x=\dfrac{1}{6}:3=\dfrac{1}{18}\)

\(x+\dfrac{13}{15}=-\dfrac{2}{5}\\ x=-\dfrac{2}{5}-\dfrac{13}{15}\\ x=-\dfrac{6}{15}-\dfrac{13}{15}\\ x=-\dfrac{19}{15}\)

\(\dfrac{7}{8}:5\times\dfrac{1}{7}\\ =\dfrac{7}{8}\times\dfrac{1}{5}\times\dfrac{1}{7}\\ =\dfrac{7\times1\times1}{8\times5\times7}\\ =\dfrac{1}{8\times5}=\dfrac{1}{40}\)

Thể tích lượng nước trong bể khi chưa lấy hòn núi giả ra là:

$8\times6\times4=192(dm^3)$

Thể tích lượng nước sau khi lấy hòn núi giả ra là:

$192-19,2=172,8(dm^3)$

Sau khi lấy hòn núi giả ra thì mực nước trong bể cao:

$172,8:8:6=3,6(dm)$

a) x - 2/3 = 1/5 : 4/5

x - 2/3 = 1/5 × 5/4

x - 2/3 = 1/4

x = 1/4 + 2/3

x = 3/12 + 8/12

x = 11/12

b) x × 3/4 = 6/5

x = 6/5 : 3/4

x = 6/5 × 4/3

x = 24/15

x = 8/5

Câu 2a;

\(x\) - \(\dfrac{2}{3}\) = \(\dfrac{1}{5}\) : \(\dfrac{4}{5}\)

\(x\) - \(\dfrac{2}{3}\) = \(\dfrac{1}{4}\)

\(x\)       = \(\dfrac{1}{4}\) + \(\dfrac{2}{3}\)

\(x\)      = \(\dfrac{11}{12}\)

Ta thấy :

\(\dfrac{3}{10}>\dfrac{3}{15}\)

\(\dfrac{3}{11}>\dfrac{3}{15}\)

\(\dfrac{3}{12}>\dfrac{3}{15}\)

\(\dfrac{3}{13}>\dfrac{3}{15}\)

\(\dfrac{3}{14}>\dfrac{3}{15}\)

\(\Rightarrow S=\dfrac{3}{10}+\dfrac{3}{11}+\dfrac{3}{12}+\dfrac{3}{13}+\dfrac{3}{14}>5.\dfrac{3}{15}\) (1)

\(S=\dfrac{3}{10}+\dfrac{3}{11}+\dfrac{3}{12}+\dfrac{3}{13}+\dfrac{1}{14}>1\)

Ta có:

\(\dfrac{3}{10}< \dfrac{3}{9}\)

\(\dfrac{3}{11}< \dfrac{3}{9}\)

\(\dfrac{3}{12}< \dfrac{3}{9}\)

\(\dfrac{3}{13}< \dfrac{3}{9}\)

\(\dfrac{3}{14}< \dfrac{3}{9}\)

\(\Rightarrow S=\dfrac{3}{10}+\dfrac{3}{11}+\dfrac{3}{12}+\dfrac{3}{13}+\dfrac{3}{14}< 5.\dfrac{3}{9}\)

\(\Rightarrow S< \dfrac{5}{3}< 2\)

giải s ta có s=1.267782218 thì lớn hơn 1 và nhỏ hơn 2 

Ta có: S_xq HHCN = (Chiều dài + chiều rộng).2.chiều cao(cm²) => = (58 + 45).2.x(cm²)= 206x(cm²).

cíu mik vs mik đang cần gấp

  \(-\dfrac{1}{12}\) < \(\dfrac{x}{24}\) < \(\dfrac{1}{8}\)

  - \(\dfrac{2}{24}\) < \(\dfrac{x}{24}\) < \(\dfrac{3}{24}\)

- 2 < \(x\) < 3

  \(x\) \(\in\) {-1; 0; 1; 2}

Vậy \(x\) \(\in\) {-1; 0; 1; 2}

Câu 7: D

Câu 8: A

Câu 9: A

Câu 10:

Số cây bút 10 bạn mua là: 10x2=20(cây)

Số tiền phải trả là:

10x3500=35000(đồng)