a: \(=\dfrac{2}{5}\cdot\dfrac{5}{6}\cdot\dfrac{3}{4}\cdot\dfrac{4}{3}=\dfrac{2}{6}=\dfrac{1}{3}\)

b: \(=\dfrac{123\cdot145+100}{123\cdot145+12\cdot145-45}=\dfrac{123\cdot145+100}{123\cdot145+1695}\)

=3587/3906

a) 160     b) 1612,8     c) 1960     d) 0,25

giõ chút

4:

a: \(=\dfrac{1}{2}\cdot\dfrac{-2}{3}x^2y\cdot xy^2=\dfrac{-1}{3}\cdot x^3y^3\)

b: \(=2xy^2\cdot\dfrac{1}{9}x^4y^6=\dfrac{2}{9}x^5y^8\)

câu 1 : có số con vật là : 5 + 3 + 4 + 9 = 21 con

                 Đ/s : 21 con

câu 2 : 

     4x5 = 20
     5x3 = 15 
     3x9 = 27 
     4x6+2 = 26

câu 1 :

trong rừng đó có số con vật là :

5 + 3 + 9 + 4 = 21 ( con )

đáp số : 21 con vật

câu 2 :

4 x 5 = 20

5 x 3 = 15

3 x 9 =27

 4 x 6 + 2 = 24 + 2 = 26

21 con

4x5=20

5x3=15

3x9=27

4x6+2=26

\(y-\dfrac{2}{3}=\dfrac{4}{5}\times\dfrac{3}{4}\\ y-\dfrac{2}{3}=\dfrac{3}{5}\\ y=\dfrac{3}{5}+\dfrac{2}{3}\\ y=\dfrac{9}{15}+\dfrac{10}{15}\\ y=\dfrac{19}{15}\)

    \(\dfrac{7}{6}\) + \(\dfrac{5}{12}\) - \(\dfrac{1}{18}\) - 1 

=  \(\dfrac{42}{36}\) + \(\dfrac{15}{36}\) - \(\dfrac{2}{36}\) - \(\dfrac{36}{36}\)

= \(\dfrac{19}{36}\)

\(\dfrac{13}{6}\) + \(\dfrac{5}{18}+3-\dfrac{7}{12}\)

= \(\dfrac{78}{36}+\dfrac{10}{36}+\dfrac{108}{36}-\dfrac{21}{36}\)

= \(\dfrac{175}{36}\)

3 + \(\dfrac{11}{4}-\dfrac{1}{12}-\dfrac{3}{16}\)

= \(\dfrac{144}{48}+\dfrac{132}{48}-\dfrac{4}{48}-\dfrac{9}{48}\)

= \(\dfrac{263}{48}\)

   \(\dfrac{2}{5}\) x \(\dfrac{7}{4}\) - \(\dfrac{2}{5}\) x \(\dfrac{3}{4}\)

=  \(\dfrac{2}{5}\) x ( \(\dfrac{7}{4}\) - \(\dfrac{3}{4}\))

= \(\dfrac{2}{5}\)  x \(\dfrac{4}{4}\)

= \(\dfrac{2}{5}\)