Bài 4:

Gọi phân số phải tìm là \(\frac{a}{10}\)  (\(a\ne0\))

Theo bài ra ta có:

\(-\frac{7}{13}< \frac{a}{10}< -\frac{4}{13}\)

\(\Rightarrow-\frac{70}{130}< \frac{-13a}{130}< -\frac{40}{130}\)

\(-70< -13a< -40\)    (1)

Do -13a chia hết cho 13 nên \(-13a\in B\left(13\right)\)    (2)

Từ (1) và (2) \(\Rightarrow\) \(-13a\in\left\{52;65\right\}\)

\(\Rightarrow a\in\left\{-4;-5\right\}\)

Vậy phân số phải tìm \(-\frac{4}{10}\)và \(-\frac{5}{10}\)

Số cây Cam là:

\(45\cdot\frac{7}{15}=21\)  (cây)

Số cây Bưởi và Chanh là:

45 - 21 = 24   (cây)

Số cây Bưởi là:

\(24\cdot\frac{5}{8}=15\) (cây)

Số cây Chanh là:

24 - 15 = 9 (cây)

           Đáp số: Cam: 21 cây

                         Bưởi: 15 cây

                         Chanh: 9 cây

Ta có:  x + y = 16

 \(5x=3y\)   \(\Rightarrow\frac{x}{3}=\frac{y}{5}\)

Áp dụng tính chất của dãy tỉ số bằng nhau ta có:

\(\frac{x}{3}=\frac{y}{5}=\frac{x+y}{3+5}=\frac{16}{8}=2\)

\(\Rightarrow\begin{cases}\frac{x}{3}=2\Rightarrow x=2\cdot3=6\\\frac{y}{5}=2\Rightarrow y=2\cdot5=10\end{cases}\)     (THỎA MÃN)

Vậy x = 6; y = 10

\(-\frac{1}{3}x^5y\left(-\frac{3}{7}\right)xy^2z\)

\(=\left[\left(-\frac{1}{3}\right)\cdot\left(-\frac{3}{7}\right)\right]x^5xyy^2z\)

\(=\frac{1}{7}x^6y^3z\)

Uncle Ho's desire was that our country might keep pace with other countries in the world.

Although David was exhausted after a day's work in the office, he tried to he help his wife the household chores

Genetically modified mosquitoes drop Zika virus can cause many consequences
 
The release of genetically modified mosquitoes into the wild to prevent disease spread by mosquitoes, such as Zika virus, malaria, dengue fever is premature and could cause unintended consequences.

 
 
This is the warning of the US scientists released on 9/6.

 
 
Professor James Collins of Arizona State University, and a co-chairman of the Commission of the national academy of science, engineering and medicine, affirmed should be cautious and conduct more studies of the consequences of social, scientific as well as the release of genetically modified organisms into the environment.

 
 
Commission warns on genetically modified technology could cause harmful effects such as reducing the number of other insects, or even more dangerous is the creation of new species capable of rapid spread of disease than.

 
 
The researchers called for further studies conducted, the tests in stages and closer collaboration between scientists.

He told her not to eat it, explaining that there was a risk of food poisoning.

1/ The distance from HCM city to Phu Quoc Island is about 300km.

\(\rightarrow\) It is about 300km from HCM city to Phu Quoc Island.

2/ Road users should obey traffic rules strictly.

\(\rightarrow\) Traffic rules should be obeyed strictly by road users.

3/ Be careful or you'll hurt yourself.

\(\rightarrow\) If you are not careful, you'll hurt yourself.