B

B

\(Ư\left(30\right)=\left\{1;2;3;5;6;10;15;30\right\}\\ \Rightarrow x=5\left(B\right)\\ B\left(8\right)=\left\{0;8;16;24;32;...\right\}\\ \Rightarrow x=24\left(B\right)\)

Câu đầu : B

Câu 2 : B

Tìm số tự nhiên x biết 

4 3/5 (4 3/5 là hỗn số) + 7/10 < x < 20/3

\(4\frac{3}{5}+\frac{7}{10}< x< \frac{20}{3}\)

\(\frac{23}{5}+\frac{7}{10}< x< \frac{20}{3}\)

\(\frac{53}{10}< x< \frac{20}{3}\)

\(\frac{159}{30}< x< \frac{200}{30}\)

Vậy \(x\in\left\{\frac{160}{30};\frac{161}{30};\frac{162}{30};...;\frac{198}{30};\frac{199}{30}\right\}\)

\(4\frac{3}{5}+\frac{7}{10}< x< \frac{20}{3}\)

\(\frac{4\times5+3}{5}+\frac{7}{10}< x>\frac{20}{3}\)

\(\frac{23}{5}+\frac{7}{10}< x< \frac{20}{3}\)

\(\frac{46}{10}+\frac{7}{10}< x< \frac{20}{3}\)

\(\frac{53}{10}< x< \frac{20}{3}\)

\(\frac{159}{30}< x< \frac{200}{30}\)

\(\Rightarrow x=\left\{160;161;162;......;199\right\}\)

\(4\frac{3}{5}+\frac{7}{10}< x< \frac{20}{3}\)

\(\frac{23}{5}+\frac{7}{10}< x< \frac{20}{3}\)

\(\frac{53}{10}< x< \frac{20}{3}\)

\(\frac{159}{30}< x< \frac{200}{30}\)

Vậy \(x=\left\{\frac{160}{30};\frac{161}{30};\frac{162}{30};\frac{163}{30};...;\frac{198}{30};\frac{199}{30}\right\}\)

nhưng đề nó bảo là số tự nhiên mà bạn.

\(4\frac{3}{5}+\frac{7}{10}< x>\frac{20}{3}\)

\(\frac{23}{5}+\frac{7}{10}< x< \frac{20}{3}\)

\(\frac{46}{10}+\frac{7}{10}< x< \frac{20}{3}\)

\(\frac{53}{10}< x< \frac{20}{3}\)

\(\frac{159}{30}< x< \frac{200}{30}\)

\(\Rightarrow x=\left\{\frac{160}{30};\frac{161}{30};....;\frac{197}{30};\frac{198}{30};\frac{199}{30}\right\}\)

x=10

10

=>80<11x<100

=>11x=88 hoặc 11x=99

=>x=8 hoặc x=9

`4/11<x/20<5/11`

`=>80/220<11x/220<100/220`

`=>80<11x<100`

`=> x=8` hoặc `x=9`