\(\dfrac{7}{21}+\dfrac{-9}{36}=\dfrac{1}{3}+\dfrac{-1}{4}=\dfrac{4}{12}+\dfrac{-3}{12}=\dfrac{1}{12}\)

\(\dfrac{-12}{18}+\dfrac{-21}{35}=\dfrac{-2}{3}+\dfrac{-3}{5}=\dfrac{-10}{15}+\dfrac{-9}{15}=\dfrac{-19}{15}\)

\(\dfrac{-18}{14}+\dfrac{15}{-21}=\dfrac{-9}{7}+\dfrac{-5}{7}=\dfrac{-14}{7}=-2\)

\(\dfrac{3}{21}+\dfrac{-6}{42}=\dfrac{1}{7}+\dfrac{-1}{7}=0\)

     Tính nhanh à

 21+22+23+24-11-12-13-14= 

=21+22+23+24+(-11)+(-12)+(-13)+(-14)

=[21+(-11)]+[22+(-12)]+[23+(-13)]+[24+(-14)]

=10+10+10+10

=40

mik làm luôn nhé

(21-11)+(22-12)+(23-13)+(24-14)

=10+10+10+10

=40

21+22+23+24-11-12-13-14

=(21-11)+(22-12)+(23+13)+(24-14)

=10 +10+10+10

=40

12/18>1/3

21/24>5/8

12/18 ... 1/3

12/18 ; 1/3 = 6/18

Vậy 12/18 > 6/18 hay 12/8 > 1/3

21/24 ...5/8

21/24 ; 5/8 = 15/24

Vậy 21/24 > 15/24 hay 21/24 > 5/8

>

>

\(a,\dfrac{5}{15}+\dfrac{2}{5}\\ =\dfrac{1}{3}+\dfrac{2}{5}\\ =\dfrac{11}{15}\\ b,\dfrac{2}{7}+\dfrac{12}{21}\\ =\dfrac{2}{7}+\dfrac{4}{7}\\ =\dfrac{6}{7}\\ c,\dfrac{16}{24}+\dfrac{5}{12}\\ =\dfrac{8}{12}+\dfrac{5}{12}\\ =\dfrac{13}{12}\)

a, 11/15                                         

b,6/7

c,13/12

a, 11/15                                         

b,6/7

c,13/1

           Số số hạng của dãy là:

                  [100-20]:1+1=81

           Tổng của dãy là:

                  [100+20].81:2=4860 

a)=9600

37

166

85

174

\(a,\frac{11}{12}:\frac{7}{24}\cdot\frac{21}{24}=\frac{11\cdot24\cdot7\cdot3}{4\cdot3\cdot7\cdot24}=\frac{11}{4}\)

\(b,\frac{5}{12}:\frac{7}{4}-\frac{25}{18}:\frac{35}{6}=\frac{5\cdot4}{3\cdot4\cdot7}-\frac{5\cdot5\cdot6}{6\cdot3\cdot5\cdot7}=\frac{5}{21}\)

Các phân số bằng 3/4 là:

\(\dfrac{45}{60};\dfrac{12}{16}\)

 6/16 , 45/60 , 21/24 , 12/16 , 8/12

3 + 6 + 9 + 12 + 15 + 18 + 21 + 24 + 27

= 135

3 + 6 + 9 + 12 + 15 + 18 + 21 + 24 + 27

= (3 + 27) + (6 + 24) + (9 + 21) + (12 + 18) + 15

=    30    +    30        + 30       + 30      + 15

= 30 x 4 + 15

= 120 + 15

= 135

3+6+9+12+15+18+21+24+27=135