Lời giải:

$\frac{1}{2}+\frac{1}{2}=\frac{1+1}{2}=\frac{2}{2}=1$

$\frac{3}{8}+\frac{1}{8}=\frac{3+1}{8}=\frac{4}{8}=\frac{1}{2}$

$\frac{7}{9}+\frac{5}{9}=\frac{7+5}{9}=\frac{12}{9}=\frac{3\times 4}{3\times 3}=\frac{4}{3}$

Sao lại = hả bạn?

 \(\dfrac{3}{5}+\dfrac{1}{2}-\dfrac{7}{10}=\dfrac{6}{10}+\dfrac{5}{10}-\dfrac{7}{10}=\dfrac{11}{10}-\dfrac{7}{10}=\dfrac{4}{10}=\dfrac{2}{5}\)

\(\dfrac{4}{7}:\dfrac{8}{11}=\dfrac{4}{7}\times\dfrac{11}{8}=\dfrac{44}{56}=\dfrac{11}{14}\)

\(\dfrac{6}{10}+\dfrac{5}{10}-\dfrac{7}{10}=\dfrac{4}{10}=\dfrac{2}{5}\)

\(\dfrac{4}{7}x\dfrac{11}{8}=\dfrac{44}{56}=\dfrac{11}{14}\)

\(\dfrac{3}{5}+\dfrac{1}{2}-\dfrac{7}{10}=\dfrac{6}{10}+\dfrac{5}{10}-\dfrac{7}{10}=\dfrac{4}{10}=\dfrac{2}{5}\)

\(\dfrac{4}{7}:\dfrac{8}{11}=\dfrac{4}{7}\times\dfrac{11}{8}=\dfrac{44}{56}=\dfrac{11}{14}\)

a, =1/4 + 5/6

=3/12 + 10/12

=13/12

\(\frac{2}{8}\)+\(\frac{5}{6}\)

=\(\frac{1}{4}\)+\(\frac{5}{6}\)

=\(\frac{6}{24}\)+\(\frac{20}{24}\)

=\(\frac{13}{12}\)

12/18_12/42

( 2/5 +3/4 ) * 2/3 - 8/15 = 23/20 * 2/3 -8/15

= 23/30 - 8/15 = 7/30

là 7/30

1, Rút gọn rồi tính 

a) \(\frac{4}{5}+\frac{3}{15}\)

= \(\frac{4}{5}+\frac{1}{5}\)

= \(\frac{5}{5}\)

= \(1\)

b) \(\frac{2}{3}+\frac{32}{24}\)

= \(\frac{2}{3}+\frac{4}{3}\)

= \(\frac{6}{3}\)

= \(2\)

c) \(\frac{5}{6}+\frac{15}{18}\)

= \(\frac{5}{6}+\frac{5}{6}\)

= \(\frac{10}{6}\)

= \(\frac{5}{3}\)

2, Tính rồi rút gọn 

a) \(\frac{8}{15}+\frac{2}{3}\)

= \(\frac{8}{15}+\frac{10}{15}\)

= \(\frac{18}{15}\)

= \(\frac{6}{5}\)

b) \(\frac{3}{7}+\frac{4}{8}\)

= \(\frac{24}{56}+\frac{28}{56}\)

= \(\frac{52}{56}\)

= \(\frac{13}{14}\)

Đáp án:

a) 1

b) 2

c) 5/3

Bài 3.Tính rồi rút gọn

a)6/5

b) 13/14

a) 4/5+3/15=4/5+1/5=1

b) 2/3+32/24=2/3+4/3=2

c)5/6+15/18=5/6+5/6=5/3

3.

a)8/15+2/3=18/15=6/5

b)3/7+4/8=52/56=13/14

Nhớ k cho mình đó !

Đã hứa thì phải làm

`2/5 + 9/15= 2/5 + 3/5=5/5=1`

`15/45 + 25/30= 1/3 + 5/6= 2/6+5/6=7/6`

`28/32 + 45/72=7/8+ 5/8=12/8=3/2`

`8/28 + 5/30= 2/7 + 1/6= 12/42 + 7/42= 19/42`

b: 12/20+6/18=3/5+1/3=9/15+5/15=14/15

c: 8/12+20/30=2/3+2/3=4/3

d: 10/12+12/36=5/6+2/6=7/6

a) \(\dfrac{5}{6}-\dfrac{2}{14}\)

\(=\dfrac{5}{6}-\dfrac{1}{7}\)

\(=\dfrac{35}{42}-\dfrac{6}{42}\)

\(=\dfrac{29}{42}\)

b) \(\dfrac{5}{20}-\dfrac{1}{6}\)

\(=\dfrac{1}{4}-\dfrac{1}{6}\)

\(=\dfrac{3}{12}-\dfrac{2}{12}\)

\(=\dfrac{1}{12}\)

c) \(\dfrac{5}{9}-\dfrac{3}{12}\)

\(=\dfrac{5}{9}-\dfrac{1}{4}\)

\(=\dfrac{20}{36}-\dfrac{9}{36}\)

\(=\dfrac{11}{36}\)

d) \(8-\dfrac{4}{6}\)

\(=\dfrac{48}{6}-\dfrac{4}{6}\)

\(=\dfrac{44}{6}=\dfrac{22}{3}\).

`8/56+3/21`

`=1/7+1/7`

`=2/7`

=1/7 + 1/7 =2/7

\(\dfrac{8}{56}+\dfrac{3}{21}\)
\(=\dfrac{1}{7}+\dfrac{1}{7}\)
\(=\dfrac{2}{7}\)