a; \(\dfrac{2}{5}\) x \(\dfrac{3}{4}\) + \(\dfrac{6}{15}\) : \(\dfrac{4}{9}\) x 5

  = \(\dfrac{3}{10}\) + \(\dfrac{2}{5}\) x \(\dfrac{9}{4}\) x 5

= \(\dfrac{3}{10}\) + \(\dfrac{9}{10}\) x 5

= \(\dfrac{3}{10}\) + \(\dfrac{45}{10}\)

= \(\dfrac{48}{10}\)

= \(\dfrac{24}{5}\)

b; \(\dfrac{25}{12}\) x \(\dfrac{18}{35}\) x \(\dfrac{63}{24}\)

=   \(\dfrac{15}{14}\) x \(\dfrac{63}{24}\)

= \(\dfrac{45}{16}\) 

c; 4\(\dfrac{1}{2}\) + \(\dfrac{1}{2}\) : 5\(\dfrac{1}{2}\)

= \(\dfrac{9}{2}\) + \(\dfrac{1}{2}\) : \(\dfrac{11}{2}\)

 = \(\dfrac{9}{2}\) + \(\dfrac{1}{11}\)

= \(\dfrac{99}{22}\) + \(\dfrac{2}{22}\)

=  \(\dfrac{101}{22}\)

Ta có :

15/27>15/30=1/2

Suy ra 15/27>1/2

1/2=12/24>11/24

Suy ra 1/2>11/24

Vậy 15/27>1/2>11/24

\(\frac{3}{15}\)= \(\frac{3:3}{15:3}\) = \(\frac{1}{5}\)

\(\frac{33}{44}\)= \(\frac{33:11}{44:11}\)= \(\frac{3}{4}\)

\(\frac{2}{8}\)= \(\frac{2:2}{8:2}\)= \(\frac{1}{4}\)

\(\frac{1}{5}\)= \(\frac{1\times4}{5\times4}\)= \(\frac{4}{20}\)

\(\frac{3}{4}\)=\(\frac{3\times5}{4\times5}\)= \(\frac{15}{20}\)

\(\frac{1}{4}\)= \(\frac{1\times5}{4\times5}\)= \(\frac{5}{20}\)

\(\frac{9}{12}\)=\(\frac{9:3}{12:3}\) = \(\frac{3}{4}\)

\(\frac{24}{36}\)=\(\frac{24:12}{36:12}\)= \(\frac{2}{3}\)

\(\frac{3}{8}\)= \(\frac{3:1}{8:1}\)= \(\frac{3}{8}\)

\(\frac{3}{4}\)=\(\frac{3\times6}{4\times6}\)= \(\frac{18}{24}\)

\(\frac{2}{3}\)=\(\frac{2\times8}{3\times8}\)=\(\frac{16}{24}\)

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

3/15= 1/5; 33/44=3/4; 2/8= 1/4

1/5= 1x 4/ 5x4= 4/20; 3/4= 3x 5/ 4x 5= 15/20; 1/4= 1x 5/ 4x 5= 5/20

9/12= 3/4; 24/36= 2/3; 3/8 không rút gọn được

3/4= 3x 6/ 4x6= 18/24; 2/3= 2x 8/ 3x 8= 16/24; 3/8= 3x 3/ 8x 3= 9/24

a, \(\frac{3}{15}=\frac{1}{5};\frac{33}{44}=\frac{3}{4};\frac{2}{8}=\frac{1}{4}\)

mcs:20

\(\frac{1}{5}=\frac{1x4}{5x4}=\frac{4}{20}:\frac{3}{4}=\frac{3x5}{4x5}=\frac{15}{20};\frac{1}{4}=\frac{1x5}{4x5}=\frac{5}{20}\)

b,\(\frac{9}{12}=\frac{3}{4};\frac{24}{36}=\frac{2}{3};\frac{3}{8}\)

msc:24

\(\frac{3}{4}=\frac{3x6}{4x6}=\frac{18}{24};\frac{2}{3}=\frac{2x8}{3x8}=\frac{16}{24};\frac{3}{8}=\frac{3x3}{8x3}=\frac{9}{34}\)

\(\frac{1}{15}\) và \(-7\)

Biết\(-7=\frac{-7}{1}\)nên MSC là : 15

Ta có:

\(\frac{1}{15}=\frac{1.1}{15.1}=\frac{1}{15}\)

\(\frac{-7}{1}=\frac{-7.15}{1.15}=\frac{-105}{15}\)

Vậy quy đồng mẫu số các phân số \(\frac{1}{15}\) và \(-7\) ta được \(\frac{1}{15}\) và \(\frac{-105}{15}\)

Ta có: 5/6=5x4/6x4=20/24

Lại có: 3/8=3x3/8x3=9/24

Câu 1:

MSC=60

7/10=7.6/10.6=42/60            5/-12=-5/12=-5.5/12.5=-25/60

Câu 2:

17/34=1/2;  -12/22=-6/11;  -25/35=-5/7;  125/75=5/3

Câu 3:

MSC=24

1/3=1.8/3.8=8/24     -3/8=-3.3/8.3=-9/24           17/24=17/24

1/6,2/6,3/6,4/6,5/6...

3/24,5/24,7/24,9/24,11/24...

4/20,5/20,6/20,7/20...

8/30,9/30,10/30,11/30..

Giúp mik đi......................

\(\dfrac{1}{2};\dfrac{2}{3};\dfrac{3}{4}=\dfrac{1}{2}=\dfrac{1\times6}{2\times6}=\dfrac{6}{12};\dfrac{2}{3}=\dfrac{2\times4}{3\times4}=\dfrac{8}{12};\dfrac{3}{4}=\dfrac{3\times3}{4\times3}=\dfrac{9}{12}\)