\(\dfrac{-2}{3}\cdot\dfrac{5}{7}+\dfrac{5}{7}:\dfrac{3}{4}-1=\dfrac{-2}{3}\cdot\dfrac{5}{7}+\dfrac{5}{7}\cdot\dfrac{4}{3}-1=\left(\dfrac{-2}{3}+\dfrac{4}{3}\right)\cdot\dfrac{5}{7}-1=\dfrac{2}{3}\cdot\dfrac{5}{7}-1=\dfrac{10}{21}-1=-\dfrac{11}{21}\)

−2 / 3⋅5 / 7+5 / 7:3 / 4−1=−2 / 3⋅5 / 7+5 / 7⋅4 / 3−1=(−2 / 3+4 / 3)⋅5 /. 7−1=2 / 3⋅5 / 7−1=10 / 21−1=−11 / 21

nha 

\(24\cdot(34-19)-34\cdot(24-19)\)

\(=24\cdot34-24\cdot19-34\cdot24-34\cdot19\)

\(=(24\cdot34-34\cdot24)-(24\cdot19-34\cdot19)\)

\(=0-(-190)=190\)

 Cách 1 :24.(34-19)-34.(24-19) =24.15-34.5

                                    =360-170

                                    =190

Cách 2 :24.(34-19)-34.(24-19) =24.34-24.19-34.24+34.19

                                                 =816-456-816+646

                                                 =360-816+646

                                                 =-456+646

                                                 =190

\(\dfrac{4}{5}\)+\(\dfrac{-5}{4}\)=\(\dfrac{0}{4}\)

\(\dfrac{-1}{3}\)+\(\dfrac{2}{5}-\dfrac{5}{6}\)=\(\dfrac{-10}{30}+\dfrac{12}{30}-\dfrac{25}{30}\)=\(\dfrac{-23}{30}\)

\(\dfrac{2}{3}-\dfrac{5}{7}.\dfrac{14}{25}\)=\(\dfrac{2}{3}-\dfrac{2}{5}\)=\(\dfrac{10}{15}-\dfrac{6}{15}\)=\(\dfrac{4}{15}\)

a: \(=\dfrac{16-25}{20}=\dfrac{-9}{20}\)

b: \(=\dfrac{-10}{30}+\dfrac{12}{30}-\dfrac{25}{30}=-\dfrac{23}{30}\)

c: \(=\dfrac{2}{3}-\dfrac{1}{5}\cdot2=\dfrac{2}{3}-\dfrac{2}{5}=\dfrac{10-6}{15}=\dfrac{4}{15}\)

d: \(=\dfrac{12-25}{30}\cdot\dfrac{15}{8}-1=\dfrac{-13}{16}-1=\dfrac{-29}{16}\)

e: \(=\dfrac{-3}{13}-\dfrac{10}{13}-\dfrac{7}{17}+\dfrac{24}{17}-\dfrac{5}{19}-\dfrac{14}{19}=-1\)

sai vì mới nhìn đã bit là toàn số chẵn nhân nhau mà bằng 1 số lẻ

Sai, vì các số hạng trong tổng đều là số chẵn nên kết quả là chẵn

Vì 12;24;52;17*4;19*2 đều là các số chẵn nên tổng của chúng cũng là 1 số chẵn mà Toàn lại làm ra =253 (1 số lả) do đó Toàn làm sai

65.(-19) + (-19).24 + (-19).11

= ( - 19) . ( 65 + 24 + 11 )                          

= ( -19) . 100 = -1900                                  

( 4/9 + 7/9 -  2/9 ) x 19/24  = 1 x 19/24 = 19/24

\(=\dfrac{19}{24}\times\left(\dfrac{4}{9}+\dfrac{7}{9}-\dfrac{2}{9}\right)=\dfrac{19}{24}\times1=\dfrac{19}{24}\)

\(\dfrac{19}{24}\times\left(\dfrac{4}{9}+\dfrac{7}{9}-\dfrac{2}{9}\right)\)

\(=\dfrac{19}{24}\times1=\dfrac{19}{24}\)

a) \(\dfrac{17}{24}\times\dfrac{3}{51}=\dfrac{51}{1224}=\dfrac{1}{24}\)

b) \(\dfrac{6}{7}\div\dfrac{24}{49}-\dfrac{1}{24}\)

\(=\dfrac{7}{4}-\dfrac{1}{24}=\dfrac{41}{24}\)

a) \(\dfrac{17}{24}\)x\(\dfrac{3}{51}=\dfrac{51}{1224}=\dfrac{1}{24}\)

b) \(\dfrac{6}{7}:\dfrac{24}{49}-\dfrac{1}{24}=\dfrac{7}{4}-\dfrac{1}{24}=\dfrac{41}{24}\)

\(B=\dfrac{13}{15}\cdot0,15\cdot3+\left(\dfrac{8}{15}-1\dfrac{19}{60}\right):\left(1\dfrac{23}{24}\right)\)

\(=\dfrac{13}{15}\cdot\dfrac{15}{100}\cdot3+\left(\dfrac{32}{60}-1-\dfrac{19}{60}\right):\dfrac{47}{24}\)

\(=\dfrac{39}{100}+\dfrac{-47}{60}\cdot\dfrac{24}{47}\)

\(=\dfrac{39}{100}-\dfrac{24}{60}=\dfrac{39}{100}-\dfrac{40}{100}=-\dfrac{1}{100}\)