Tính:

2/7 + 5/7=1          

8/15 + 6/15 =14/15         

2/9 + 3/9 + 4/9=9/9=1

[ Không cần làm phép tính ]Điền vào ô trống <,>,= :

3/5 + 1/5 = 1/5 + 3/5

7/9 + 1/9 < 7/9 + 1/9 + 1/9

3/7 + 2/7 < 3/7 + 4/7

1/5 + 3/5 < 2/5 + 3/5

Tính:

2/7 + 5/7=1          

8/15 + 6/15 =14/15         

2/9 + 3/9 + 4/9=9/9=1

[ Không cần làm phép tính ]Điền vào ô trống <,>,= :

3/5 + 1/5 = 1/5 + 3/5

7/9 + 1/9 < 7/9 + 1/9 + 1/9

3/7 + 2/7 < 3/7 + 4/7

1/5 + 3/5 < 2/5 + 3/5

8 + 1 = 9     7 + 2 = 9     6 + 3 = 9     5 + 4 = 9

1 + 8 = 9     2 + 7 = 9     3 + 6 = 9     4 + 5= 9

9 - 8 = 1     9 - 7 = 2     9 - 6 = 3     9 - 5 = 4

9 - 1 = 8     9 - 2 = 7     9 - 3 = 6     9 - 4 = 5

Ta có: \(\dfrac{3}{4}-\left[\left(-\dfrac{3}{5}\right)-\left(\dfrac{1}{12}+\dfrac{2}{9}\right)-\left(-\dfrac{2}{9}-\dfrac{5}{3}\right)\right]\)

\(=\dfrac{3}{4}-\left(-\dfrac{3}{5}-\dfrac{1}{12}-\dfrac{2}{9}+\dfrac{2}{9}+\dfrac{5}{3}\right)\)

\(=\dfrac{3}{4}+\dfrac{3}{5}+\dfrac{1}{12}-\dfrac{5}{3}\)

\(=\dfrac{45}{60}+\dfrac{36}{60}+\dfrac{5}{60}-\dfrac{100}{60}\)

\(=\dfrac{-14}{60}=\dfrac{-7}{30}\)

9/15 x 5/9 - 3/5 x 2/9 + 3/5

= 1/3 - 2/15 + 3/5

= 1/5 + 3/5

= 4/5

Lời giải chi tiết:

8 + 1 = 9     7 + 2 = 9     6 + 3 = 9     5 + 4 = 9

9 - 1 = 8     9 - 2 = 7     9 - 3 = 6     9 - 4 = 5

9 - 8 = 1     9 - 7 = 2     9 - 6 = 3     9 - 5 = 4

\(\dfrac{2}{9}+\dfrac{3}{9}=\dfrac{5}{9}\)
\(\dfrac{3}{15}+\dfrac{5}{5}=\dfrac{1}{5}+\dfrac{5}{5}=\dfrac{6}{5}\)
\(\dfrac{4}{25}+\dfrac{3}{100}=\dfrac{16}{100}+\dfrac{3}{100}=\dfrac{19}{100}\)
\(\dfrac{4}{9}+\dfrac{3}{2}=\dfrac{8}{18}+\dfrac{27}{18}=\dfrac{35}{18}\)

`2/9 +3/9=(2+3)/9=5/9`

`3/15 + 5/5 = 3/15 + 15/15 = 18/15`

`4/25 + 3/100= 16/100 + 3/100= 19/100`

`4/9 + 3/2= 8/18+ 27/18= 35/18`

Chọn A