a) \(\dfrac{x-7}{5}=\dfrac{9}{15}\)

\(\dfrac{3\times\left(x-7\right)}{15}=\dfrac{9}{15}\)

3 x (X-7)=9

X - 7 = 3

X = 10

b) \(\dfrac{4+x}{10}=\dfrac{21}{30}\)

\(\dfrac{4+x}{10}=\dfrac{7}{10}\)

4+x=7

x=3

\(\dfrac{x-7}{5}=\dfrac{9}{15}\)

\(15\times(x-7)=45\)

\(15\times x-105=45\)

\(15\times x=150\)

\(x=10\)

_______________________________________

\(\dfrac{4+x}{10}+\dfrac{21}{30}\)

\(30\times(4+x)=210\)

\(120+30 \times x=210\)

\(30\times x=90\)

\(x=3\)

a. MSC = 63

 \(\dfrac{4}{7}=\dfrac{4\times9}{7\times9}=\dfrac{36}{63}\)

\(\dfrac{7}{9}=\dfrac{7\times7}{9\times7}=\dfrac{49}{63}\)

b. MSC = 18

\(\dfrac{5}{6}=\dfrac{5\times3}{6\times3}=\dfrac{15}{18}\)

\(\dfrac{17}{18}=\dfrac{17\times1}{18\times1}=\dfrac{17}{18}\)

c. MSC = 24

\(\dfrac{3}{8}=\dfrac{3\times3}{8\times3}=\dfrac{9}{24}\)

\(\dfrac{7}{12}=\dfrac{7\times2}{12\times2}=\dfrac{14}{24}\)

\(x+3 \times(x-6)=0\)

\(x+3 \times x-18=0\)

\(4\times x=18\)

\(x=18:4\)

\(x=\dfrac{9}{2}\)

$x+3\times (x-6)=0$

$x+3\times x-18=0$

$4\times x=18$

$x=18:4$

x=\dfrac{9}{2}x=29​
 

Bạn tham khảo nhé.

. là dấu nhân nha.

\(\dfrac{224224}{192192}=\dfrac{224\times1001}{192\times1001}=\dfrac{224}{192}=\dfrac{32\times7}{32\times6}=\dfrac{7}{6}\)

\(\dfrac{1818}{3232}=\dfrac{9\times202}{16\times202}=\dfrac{9}{16}\)

\(\dfrac{20062006}{20042004}=\dfrac{2006\times10001}{2004\times10001}=\dfrac{2006}{2004}=\dfrac{1003\times2}{1002\times2}=\dfrac{1003}{1002}\)

18/30;54/90

18 / 30                          ;                          54 / 90

Ta có:

\(\dfrac{32}{21}\times\dfrac{49}{45}\div\dfrac{16}{22}\times\dfrac{15}{33}=\)\(\dfrac{32}{21}\times\dfrac{49}{45}\times\dfrac{22}{16}\times\dfrac{15}{33}=\)

\(=\dfrac{32}{21}\times\dfrac{49}{45}\times\dfrac{22}{16}\times\dfrac{15}{33}\)\(=\dfrac{16\times2}{7\times3}\times\dfrac{7\times7}{3\times3\times5}\times\dfrac{11\times2}{16}\times\dfrac{5\times3}{11\times3}\)

\(=\dfrac{2}{3}\times\dfrac{7}{3}\times\dfrac{2}{1}\times\dfrac{1}{3}=\dfrac{28}{9}\)

Bạn tham khảo nhé.

$\frac{32}{21}\times \frac{49}{45}:\frac{16}{22}\times \frac{15}{22}$

$=\frac{14}{9}:\frac{16}{22}\times \frac{15}{22}$

$=\frac{77}{36}\times \frac{15}{22}$

$=\frac{35}{24}$

\(\dfrac{18}{30}=\dfrac{6\times3}{6\times5}=\dfrac{3}{5}\)

\(\dfrac{64}{80}=\dfrac{16\times4}{16\times5}=\dfrac{4}{5}\)

\(\dfrac{36}{27}=\dfrac{9\times4}{9\times3}=\dfrac{4}{3}\)

\(\dfrac{45}{35}=\dfrac{5\times9}{5\times7}=\dfrac{9}{7}\)

18/30 = 3/5 ; 64/80 = 4/5 ; 36/27 = 4/3 ; 45/35 = 9/7

Chiều dài mảnh vườn là: \(60:(2+1)\times 2=40(m)\)

Chiều rộng mảnh vườn là: \(60-40=20(m)\)

Diện tích mảnh vườn là: \(40 \times 20=800(m^2)\)

800 m2

\(\dfrac{7}{12}\)và\(\dfrac{11}{18}\)

Ta có: \(\dfrac{7}{12}=\dfrac{7\times18}{12\times18}=\dfrac{126}{216}\)

          \(\dfrac{11}{18}=\dfrac{11\times12}{18\times12}=\dfrac{132}{216}\)

126/216 và 132/216

16/18; 15/18; 17/18

viet tat cac phan so nho hon  co mau so la 212 va tu so lon hon 204