jhbmjbnhm b

\(a,\frac{42}{25}:\frac{y}{5}=\frac{6}{5}\)

\(\frac{y}{5}=\frac{42}{25}:\frac{6}{5}\)

\(\frac{y}{5}=\frac{42}{25}\times\frac{5}{6}\)

\(\frac{y}{5}=\frac{7}{5}\)

\(\Leftrightarrow5y=7.5\)

\(5y=35\)

\(y=7\)

\(b,\frac{24}{y}:\frac{8}{3}=\frac{3}{5}\)

\(\frac{24}{y}=\frac{3}{5}\times\frac{8}{3}\)

\(\frac{24}{y}=\frac{8}{5}\)

\(\Leftrightarrow8y=24.5\)

\(8y=120\)

\(y=15\)

\(\frac{5}{6}y=\frac{3}{2}\)

\(y=\frac{3}{2}:\frac{5}{6}\)

\(y=\frac{3}{2}\times\frac{6}{5}\)

\(y=\frac{9}{5}\)

\((x-6)(3x-9)>0\)
TH1:
\(\orbr{\begin{cases}x-6< 0\\3x-9< 0\end{cases}}\)\(\Rightarrow\orbr{\begin{cases}x< 6\\x< 3\end{cases}}\)\(\Rightarrow x< 3\)
TH2:
\(\orbr{\begin{cases}x-6>0\\3x-9>0\end{cases}}\)\(\Rightarrow\orbr{\begin{cases}x>6\\x>3\end{cases}}\)\(\Rightarrow x>6\)
Vậy \(x< 3\) hoặc \(x>6\)thì \((x-6)(3x-9)>0\)
Học tốt!

20.
\((2x-1)(6-x)>0\)
TH1:
\(\orbr{\begin{cases}2x-1>0\\6-x>0\end{cases}\Rightarrow\orbr{\begin{cases}x< \frac{1}{2}\\x< 6\end{cases}}\Rightarrow x< 6}\)
TH2
\(\orbr{\begin{cases}2x-1< 0\\6-x< 0\end{cases}\Rightarrow\orbr{\begin{cases}x>\frac{1}{2}\\x>6\end{cases}}\Rightarrow x>\frac{1}{2}}\)
Vậy \(x< 6\)hoặc \(x>\frac{1}{2}\)thì \((2x-1)(6-x)>0\)
 

21.
\((2-x)(x+7)< 0\)
TH1.
\(\orbr{\begin{cases}2-x>0\\x+7< 0\end{cases}\Rightarrow\orbr{\begin{cases}x< 2\\x>-7\end{cases}}\Rightarrow-7< x< 2}\)
TH2.
\(\orbr{\begin{cases}2-x< 0\\x+7>0\end{cases}\Rightarrow\orbr{\begin{cases}x>2\\x< -7\end{cases}}\Rightarrow2< x< -7}\)(vô lí)
Vậy \(-7< x< 2\) thì \((2-x)(x+7)< 0\)
 

24/y=3/5*8/3

24/y=8/5

24:y=8/5

y=24;8/5

y=15

b,42/25:y/5=6/7

y/5=42/25:6/7

y/5=49/25

y:5=49/25

y=49/25*5

y=49/5=9,8

\(\frac{24}{y}:\frac{8}{3}=\frac{3}{5}\)

\(\Rightarrow\frac{24}{y}=\frac{3}{5}\times\frac{8}{3}\)

\(\Rightarrow\frac{24}{y}=\frac{8}{5}\)

\(\Rightarrow y=\frac{8}{5}\times24=\frac{192}{5}\)

b , \(\frac{42}{25}:\frac{y}{5}=\frac{6}{7}\)

\(\Rightarrow\frac{y}{5}=\frac{6}{7}\times\frac{42}{25}=\frac{36}{25}\)

\(\Rightarrow y=\frac{36}{25}\times5=\frac{36}{5}\)

\(\frac{24}{y}:\frac{8}{3}=\frac{3}{5}\)                \(\frac{42}{25}:\frac{y}{5}=\frac{6}{7}\)

\(\frac{24}{y}=\frac{3}{5}\cdot\frac{8}{3}\)                      \(\frac{y}{5}=\frac{42}{25}:\frac{6}{7}\)

\(\frac{24}{y}=\frac{8}{5}\)                                \(\frac{y}{5}=\frac{42}{25}\cdot\frac{7}{6}\)

\(\Rightarrow8y=24\cdot5\)                         \(\frac{y}{5}=\frac{49}{25}\)

\(8y=120\)                                 \(\Rightarrow25y=5\cdot49\)

\(y=15\)                                            \(25y=245\)

                                                                \(y=\frac{49}{5}\) 

\(\frac{x-2}{27}+\frac{x-3}{26}+\frac{x-4}{25}+\frac{x-5}{24}+\frac{x-44}{5}=1\)

\(\Leftrightarrow\left(\frac{x-2}{27}-1\right)+\left(\frac{x-3}{26}-1\right)+\left(\frac{x-4}{25}-1\right)+\left(\frac{x-5}{24}-1\right)\)\(+\left(\frac{x-44}{5}+3\right)=1-1\)

\(\Leftrightarrow\frac{x-29}{27}+\frac{x-29}{26}+\frac{x-29}{25}+\frac{x-29}{24}\)\(+\frac{x-29}{5}=0\)

\(\Leftrightarrow\left(x-29\right)\left(\frac{1}{27}+\frac{1}{26}+\frac{1}{25}+\frac{1}{24}+\frac{1}{5}\right)=0\)

Mà \(\frac{1}{27}+\frac{1}{26}+\frac{1}{25}+\frac{1}{24}+\frac{1}{5}\ne0\)

=> x - 29 = 0

=> x = 29.

25 giờ 24 phút – y =20 giờ 25phút

                           y = 25g24p - 20g25p

                           y=4g59p

25 giờ 24 phút   -   y   =   4 giờ 45 phút   x   5

25 giờ 24 phút   -   y   =       23 giờ 45 phút

                               y   =   25 giờ 24 phút  -   23 giờ 45 phút

                               y   =          1 giờ 39 phút

a,\(\dfrac{6}{2x+1}=\dfrac{2}{7}\)

⇒\(\dfrac{6}{2x+1}=\dfrac{6}{21}\)

⇒\(2x+1=21\)

\(2x=21-1\)

\(2x=20\)

⇒\(x=10\)