\(\dfrac{5}{8}\) x 4 + \(\dfrac{5}{8}\) x \(\dfrac{4}{5}\)

= \(\dfrac{5}{8}\) x (\(4\) + \(\dfrac{4}{5}\) )

= \(\dfrac{5}{8}\) x \(\dfrac{24}{5}\) = 3

\(\dfrac{5}{8}\times4+\dfrac{5}{8}\times\dfrac{4}{5}\)
\(=\dfrac{5}{8}\times\left(4+\dfrac{4}{5}\right)\)
\(=\dfrac{5}{8}\times\dfrac{24}{5}\)
\(=\dfrac{24}{8}\)
\(=3\)

5/8 * 4 + 5/8 * 4/5 

= 5/8 * (4+4/5)

= 5/8 * 24/5

= 3

32 nha

1-1-0+8x4=0+32=32 nha!

0+32=32

h đúng cho minh

\(\frac{7}{9}+\frac{6}{7}\times\frac{4}{5}=\frac{7}{9}+\frac{24}{35}=\frac{361}{315}\)

\(\frac{21}{23}+\frac{4}{5}:\frac{6}{8}=\frac{21}{23}+\frac{16}{15}=\frac{548}{345}\)

\(\frac{5}{8}\times\frac{4}{9}:\frac{2}{3}=\frac{5}{18}:\frac{2}{3}=\frac{5}{12}\)

\(\frac{7}{12}+\frac{5}{6}-\frac{21}{24}=\frac{14}{24}+\frac{20}{24}-\frac{21}{24}=\frac{11}{24}\)

b, 

    \(\frac{21}{23}+\frac{4}{5}:\frac{6}{8}=\frac{21}{23}+\frac{4}{5}.\frac{8}{6}=\frac{21}{23}+\frac{16}{15}=1\frac{338}{345}\)

c,

    \(\frac{5}{8}.\frac{4}{9}.\frac{3}{2}=\frac{5}{12}\)

d,

    \(\frac{7}{12}+\frac{5}{6}-\frac{21}{24}=\frac{14}{24}+\frac{20}{24}-\frac{21}{24}=\frac{13}{24}\)

chán thật 

A = 1/3×5 + 1/5×7 + 1/7×9 + 1/9×11 + ... + 1/29×31

2A = 2/3×5 + 2/5×7 + 2/7×9 + 2/9×11 + ... + 2/29×31

2A = 1/3 - 1/5 + 1/5 - 1/7 + 1/7 - 1/9 + 1/9 - 1/11 + .... + 1/29 - 1/31

2A = 1/3 - 1/31

2A = 31/93 - 3/93 = 28/93

A = 28/93 : 2

A = 28/93 × 1/2 = 14/93

B = 2/1×4 + 2/4×7 + 2/7×10 + ... + 2/31×34

3/2B = 3/1×4 + 3/4×7 + 3/7×10 + ... + 3/31×34

3/2B = 1 - 1/4 + 1/4 - 1/7 + 1/7 - 1/10 + ... + 1/31 - 1/34

3/2B = 1 -1/34 = 33/34

B = 33/34 : 3/2

B = 33/34 × 2/3 = 11/17

\(A=\frac{1}{3\times5}+\frac{1}{5\times7}+\frac{1}{7\times9}+...+\frac{1}{29\times31}\)

   \(=\frac{1}{2}\times\left(\frac{1}{3}-\frac{1}{5}\right)+\frac{1}{2}\times\left(\frac{1}{5}-\frac{1}{7}\right)+...+\frac{1}{2}\times\left(\frac{1}{29}-\frac{1}{31}\right)\)

   \(=\frac{1}{2}\times\left(\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+...+\frac{1}{29}-\frac{1}{31}\right)\)

   \(=\frac{1}{2}\times\left(\frac{1}{3}-\frac{1}{31}\right)\)

   \(=\frac{1}{2}\times\frac{28}{93}\)

   \(=\frac{14}{93}\)

\(B=\frac{2}{1\times4}+\frac{2}{4\times7}+...+\frac{2}{31\times34}\)

   \(=\frac{1}{3}\times\left(\frac{2}{1}-\frac{2}{4}\right)+\frac{1}{3}\times\left(\frac{2}{4}-\frac{2}{7}\right)+...+\frac{1}{3}\times\left(\frac{2}{31}-\frac{2}{34}\right)\)

   \(=\frac{1}{3}\times\left(2-\frac{2}{4}+\frac{2}{4}-\frac{2}{7}+...+\frac{2}{31}-\frac{2}{34}\right)\)

   \(=\frac{1}{3}\times\left(2-\frac{2}{34}\right)\)

   \(=\frac{1}{3}\times\frac{33}{17}\)

   \(=\frac{11}{17}\)

a) \(2+\dfrac{3}{4}\)

\(=\dfrac{8}{4}+\dfrac{3}{4}\)

\(=\dfrac{8+3}{4}\)

\(=\dfrac{11}{4}\)

b) \(\dfrac{1}{3}+\dfrac{3}{2}-\dfrac{7}{4}\)

\(=\dfrac{4}{12}+\dfrac{18}{12}-\dfrac{21}{12}\)

\(=\dfrac{4+18-21}{12}\)

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

c) \(\dfrac{1}{6}+\dfrac{3}{8}-\dfrac{1}{4}\)

\(=\dfrac{4}{24}+\dfrac{9}{24}-\dfrac{6}{24}\)

\(=\dfrac{4+9-6}{24}\)

\(=\dfrac{7}{24}\)

d) \(\dfrac{5}{12}+\dfrac{3}{8}\times\dfrac{4}{9}\)

\(=\dfrac{5}{12}+\dfrac{3\times4}{8\times9}\)

\(=\dfrac{5}{12}+\dfrac{1}{6}\)

\(=\dfrac{5}{12}+\dfrac{2}{12}\)

\(=\dfrac{7}{12}\)

e) \(\dfrac{4}{5}-\dfrac{1}{5}\times\dfrac{7}{2}\)

\(=\dfrac{4}{5}-\dfrac{1\times7}{5\times2}\)

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

\(=\dfrac{8}{10}-\dfrac{7}{10}\)

\(=\dfrac{8-7}{10}\)

\(=\dfrac{1}{10}\)

f) \(\dfrac{16}{9}-\dfrac{4}{15}:\dfrac{2}{5}\)

\(=\dfrac{16}{9}-\dfrac{4}{15}\times\dfrac{5}{2}\)

\(=\dfrac{16}{9}-\dfrac{4\times5}{15\times2}\)

\(=\dfrac{16}{9}-\dfrac{2}{3}\)

\(=\dfrac{16}{9}-\dfrac{6}{9}\)

\(=\dfrac{16-6}{9}\)

\(=\dfrac{10}{9}\)

a: =8/4+3/4=11/4

b: =4/12+18/12-21/12=1/12

c: =4/24+9/24-6/24=7/24

d: =5/12+12/72

=5/12+1/6

=5/12+2/12=7/12

e: =4/5-7/10

=8/10-7/10=1/10

f: =16/9-4/15*5/2

=16/9-20/30

=16/9-2/3

=16/9-6/9=10/9

`@` `\text {Ans}`

`\downarrow`

`a,`

`2 + 3/4`

`= 8/4 + 3/4`

`= 11/4`

`b,`

`1/3 + 3/2 - 7/4`

`= 4/12 + 18/12 - 21/12`

`= 1/12`

`c,`

`1/6 + 3/8 - 1/4`

`= 4/24 + 9/24 - 6/24`

`=7/24`

`d,`

`5/12+3/8  \times 4/9`

`= 5/12 + 27/32`

`= 121/96`

`e,`

`4/5-1/5 \times 7/2`

`= 4/5 - 2/35`

`=26/35`

`f,`

`16/9-4/15 \div 2/5`

`= 16/9 - 2/3`

`= 10/9`

$#KDN040510$

\(\dfrac{3}{4}\times\dfrac{5}{7}=\dfrac{15}{28};\dfrac{5}{8}\times\dfrac{4}{15}=\dfrac{20}{120}=\dfrac{1}{6};\dfrac{7}{12}\times\dfrac{4}{9}=\dfrac{28}{108}=\dfrac{7}{27};\)

\(\dfrac{1}{6}\times\dfrac{3}{5}=\dfrac{3}{30}=\dfrac{1}{10};\dfrac{12}{21}\times\dfrac{23}{8}=\dfrac{276}{168}=\dfrac{23}{14};\dfrac{13}{4}\times\dfrac{5}{39}=\dfrac{65}{156}=\dfrac{5}{12}\)

\(\dfrac{7}{42}\times\dfrac{13}{21}=\dfrac{91}{882}=\dfrac{13}{126};\dfrac{3}{16}\times\dfrac{4}{15}=\dfrac{12}{240}=\dfrac{1}{20}\)

a)=1x2x3x4x5/2x3x4x5x6 =1/6

b)=1x2x3x4x5x6x7x8x9/10x9x8x7x6x5x4x3 x2=1/10