\(x:12=x:27\Rightarrow\dfrac{x}{12}=\dfrac{x}{27}\Rightarrow x\in\varnothing\)

65 kg=0,065 tấn

65 kg= 65:1000=0,065 tấn 

Chúc bn hok tốt nha!!!

Bài 2:

1.

$=(\frac{1}{7}+\frac{2}{7}+\frac{4}{7})+(\frac{3}{11}+\frac{8}{11})+2010$

$=\frac{7}{7}+\frac{11}{11}+2010=1+1+2010=2012$
2.

$=(\frac{2}{3}-\frac{2}{3})+(\frac{-3}{4}+\frac{3}{4})+(\frac{4}{5}-\frac{4}{5})+(\frac{-5}{6}+\frac{5}{6})+(\frac{6}{7}-\frac{6}{7})+(\frac{-7}{8}+\frac{7}{8})+\frac{1}{2012}$

$=0+0+0+0+0+0+\frac{1}{2012}=\frac{1}{2012}$

3.

$=\frac{1}{5-4}{4.5}+\frac{6-5}{5.6}+\frac{7-6}{6.7}+...+\frac{1}{20-19}{19.20}$

$=\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}+..+\frac{1}{19}-\frac{1}{20}$

$=\frac{1}{4}-\frac{1}{20}=\frac{1}{5}$

4.

\(=182\left[\frac{1+\frac{1}{5}-\frac{2}{7}+\frac{5}{13}}{2(1+\frac{1}{5}-\frac{2}{7}+\frac{5}{13})}: \frac{4(1-\frac{1}{33}-\frac{1}{57}+\frac{1}{7000})}{1-\frac{1}{33}-\frac{1}{57}+\frac{1}{7000}}\right]:\frac{10101\times 91}{10101\times 80}\)

$=182(\frac{1}{2}:4):\frac{91}{80}=182\times \frac{1}{8}\times \frac{80}{91}$

$=\frac{91\times 2\times 80}{8\times 91}=\frac{160}{8}=20$

a) \(=1-\dfrac{1}{2}+\dfrac{1}{2}-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{4}+\dfrac{1}{4}-\dfrac{1}{5}+...+\dfrac{1}{9}-\dfrac{1}{10}\)

\(=1-\dfrac{1}{10}=\dfrac{9}{10}\)

b) \(=\dfrac{1}{3x4}+\dfrac{1}{4x5}+\dfrac{1}{5x6}+\dfrac{1}{6x7}+\dfrac{1}{7x8}+\dfrac{1}{8x9}+\dfrac{1}{9x10}\)

\(=\dfrac{1}{3}-\dfrac{1}{4}+\dfrac{1}{4}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{6}+\dfrac{1}{6}-\dfrac{1}{7}+\dfrac{1}{7}-\dfrac{1}{8}+\dfrac{1}{8}-\dfrac{1}{9}+\dfrac{1}{9}-\dfrac{1}{10}\)

\(=\dfrac{1}{3}-\dfrac{1}{10}=\dfrac{10}{30}-\dfrac{3}{30}=\dfrac{7}{30}\)

(6+12):2=9(h)

Vận tốc thanh niên 1 chạy :

\(600:\left(15x60\right)=\dfrac{2}{3}\left(m/s\right)\)

Vận tốc thanh niên 2 chạy :

\(230:32=\dfrac{115}{16}\left(m/s\right)\)

Vận tốc thanh niên 3 chạy :

\(450:\left(3x60\right)=\dfrac{5}{2}\left(m/s\right)\)

Bài 1:

1. $\frac{4}{15}+\frac{11}{15}=\frac{4+11}{15}=\frac{15}{15}=1$

2. $\frac{5}{6}+\frac{14}{12}=\frac{5}{6}+\frac{7}{6}=\frac{5+7}{6}=\frac{12}{6}=2$
3. $3+\frac{3}{5}=\frac{15}{5}+\frac{3}{5}=\frac{18}{5}$

4. $\frac{15}{13}-\frac{2}{13}=\frac{13}{13}=1$

5. $\frac{3}{4}-\frac{1}{3}=\frac{9}{12}-\frac{4}{12}=\frac{5}{12}$
 

Bài 1:

6.

$\frac{3}{5}-\frac{6}{15}=\frac{3}{5}-\frac{2}{5}=\frac{1}{5}$

7.

$\frac{18}{5}-3=\frac{18}{5}-\frac{15}{5}=\frac{3}{5}$

8.

$7-\frac{5}{7}=\frac{49}{7}-\frac{5}{7}=\frac{44}{7}$
9.

$\frac{6}{7}\times \frac{14}{36}=\frac{6\times 14}{7\times 36}=\frac{6\times 7\times 2}{7\times 7\times 6}=\frac{2}{6}=\frac{1}{3}$

10.

$3\times \frac{7}{9}=\frac{3\times 7}{3\times 3}=\frac{7}{3}$

=>\(D=7\left(\dfrac{5}{42\cdot37}+\dfrac{1}{42\cdot43}+\dfrac{6}{43\cdot49}+\dfrac{10}{49\cdot59}\right)\)

\(=7\left(\dfrac{1}{37}-\dfrac{1}{42}+\dfrac{1}{42}-\dfrac{1}{43}+\dfrac{1}{43}-\dfrac{1}{49}+\dfrac{1}{49}-\dfrac{1}{59}\right)\)

=7(1/37-1/59)

=7*22/2183

\(E=5\left(\dfrac{8}{37\cdot45}+\dfrac{2}{45\cdot47}+\dfrac{3}{47\cdot50}+\dfrac{9}{50\cdot59}\right)\)

\(=5\left(\dfrac{1}{37}-\dfrac{1}{45}+\dfrac{1}{45}-\dfrac{1}{47}+...+\dfrac{1}{50}-\dfrac{1}{59}\right)\)

=5(1/37-1/59)

=>D/E=7/5

ờ bn ơi

f) \(\left(x-1\right)\left(x-2\right)=0\)

\(\Rightarrow\left[{}\begin{matrix}x-1=0\\x-2=0\end{matrix}\right.\)

\(\Rightarrow\left[{}\begin{matrix}x=1\\x=2\end{matrix}\right.\)

Vậy: \(S=\left\{1;2\right\}\)

Thời gian ô tô đi từ A đến B là:

11 giờ 20 phút - 6 giờ 20 phút = 5 giờ

Vận tốc của ô tô là:

\(120:5=24\left(km/h\right)\)

Đáp số: ...

Thời gian ô tô đi từ A đến B là:

11 giờ 20 phút - 6 giờ 20 phút = 5 giờ

Vận tốc của ô tô là: