a: =5*1,4-4*1,5+3*1,3

=7-6+3,9=4,9

b: =1/3*7+3/4*18-2/3*20

=7/3+54/4-40/3

=-11+54/4

=2,5

c: =5/6*17-1/2*16+2/5*15

=85/6-8+6

=85/6-2

=73/6

d: =15*4/5+12*3/4-18*4/9

=12+9-8

=12+1=13

cách giải bài này như nào: 5/20+1/4+6/24+8/32=bao nhiêu

    \(\dfrac{4}{5}\) : (\(\dfrac{4}{5}\) .- \(\dfrac{5}{4}\)) : (\(\dfrac{16}{25}\) - \(\dfrac{1}{5}\))

=  \(\dfrac{4}{5}\) : (-1) : (\(\dfrac{16}{25}\) - \(\dfrac{5}{25}\))

= -\(\dfrac{4}{5}\)  : \(\dfrac{11}{25}\)

= - \(\dfrac{4}{5}\) x \(\dfrac{25}{11}\)

=  - \(\dfrac{20}{11}\)

    \(\dfrac{11}{12}\) : (\(\dfrac{7}{9}\) + \(\dfrac{-1}{3}\)) - (\(\dfrac{2}{3}\) - \(\dfrac{5}{15}\))

= \(\dfrac{11}{12}\) : (\(\dfrac{7}{9}\) - \(\dfrac{3}{9}\)) - (\(\dfrac{2}{3}\) - \(\dfrac{1}{3}\))

= \(\dfrac{11}{12}\) : \(\dfrac{4}{9}\) - \(\dfrac{1}{3}\)

= \(\dfrac{11}{12}\) x \(\dfrac{9}{4}\) - \(\dfrac{1}{3}\)

= \(\dfrac{99}{48}\) - \(\dfrac{1}{3}\)

= \(\dfrac{99}{48}\) - \(\dfrac{16}{48}\)

= \(\dfrac{83}{48}\)  

\(\dfrac{4}{5}\): (\(\dfrac{4}{5}\).-\(\dfrac{5}{4}\)) : (\(\dfrac{16}{25}\) - \(\dfrac{1}{5}\))

=\(\dfrac{4}{5}\) x - 1: (\(\dfrac{16}{25}\) - \(\dfrac{5}{25}\))

= - \(\dfrac{4}{5}\) : \(\dfrac{11}{25}\)

= - \(\dfrac{4}{5}\) x \(\dfrac{25}{11}\)

= - \(\dfrac{20}{11}\) 

\(\dfrac{11}{12}\): (\(\dfrac{7}{9}\) + - \(\dfrac{1}{3}\)) - (\(\dfrac{2}{3}\) - \(\dfrac{5}{15}\))

= \(\dfrac{11}{12}\) : (\(\dfrac{7}{9}\) - \(\dfrac{3}{9}\)) - (\(\dfrac{2}{3}\) - \(\dfrac{1}{3}\))

= \(\dfrac{11}{12}\) : \(\dfrac{4}{9}\) - \(\dfrac{1}{3}\)

= \(\dfrac{11}{12}\) x \(\dfrac{9}{4}\) - \(\dfrac{1}{3}\)

= \(\dfrac{99}{48}\) - \(\dfrac{16}{48}\)

= \(\dfrac{83}{48}\) 

- \(\dfrac{2}{5}\).(\(\dfrac{9}{8}\) + \(\dfrac{16}{32}\) - \(\dfrac{3}{4}\)) - \(\dfrac{9}{10}\)

= - \(\dfrac{2}{5}\).(\(\dfrac{9}{8}\) + \(\dfrac{4}{8}\) - \(\dfrac{6}{8}\)) - \(\dfrac{9}{10}\)

= - \(\dfrac{2}{5}\).(\(\dfrac{13}{8}\) - \(\dfrac{6}{8}\)) - \(\dfrac{9}{10}\)

= - \(\dfrac{2}{5}\).\(\dfrac{7}{8}\) - \(\dfrac{9}{10}\)

= - \(\dfrac{7}{20}\) - \(\dfrac{18}{20}\)

= - \(\dfrac{5}{4}\)

a)\(=\dfrac{16}{13}-\dfrac{3}{15}+\dfrac{6}{13}=\dfrac{22}{13}-\dfrac{3}{15}=\dfrac{96}{65}\)

b)\(=\dfrac{21}{8}-\left(\dfrac{5}{10}+\dfrac{6}{10}\right)=\dfrac{21}{8}-\dfrac{11}{10}=\dfrac{61}{40}\)

c)\(=\dfrac{27}{10}-3-\dfrac{4}{7}--\dfrac{61}{70}\)

d)\(=\dfrac{576}{702}=\dfrac{4}{5}\)

e)\(=\left(\dfrac{20}{15}-\dfrac{12}{15}\right)\times\dfrac{25}{2}=\dfrac{8}{15}\times\dfrac{25}{2}=\dfrac{20}{3}\)

f)\(=\dfrac{24}{12}-\dfrac{4}{12}-\dfrac{6}{12}-\dfrac{2}{12}-\dfrac{3}{12}=\dfrac{9}{12}=\dfrac{3}{4}\)

d) \(=\dfrac{32}{45}x\dfrac{18}{16}=\dfrac{576}{720}=\dfrac{115}{114}\)

e) \(=\left(\dfrac{4}{3}-\dfrac{4}{5}\right)x\dfrac{25}{12}=\dfrac{8}{15}x\dfrac{25}{12}=\dfrac{200}{180}=\dfrac{10}{9}\)

f) \(=\dfrac{2}{1}-\dfrac{1}{3}-\dfrac{1}{2}-\dfrac{1}{6}-\dfrac{3}{12}=\dfrac{24}{12}-\dfrac{4}{12}-\dfrac{6}{12}-\dfrac{2}{12}-\dfrac{3}{12}\)

\(=\dfrac{20}{12}-\dfrac{4}{12}-\dfrac{3}{12}=\dfrac{16}{12}-\dfrac{3}{12}=\dfrac{13}{12}\)

a)\(\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+\frac{1}{4.5}+...+\frac{1}{98.99}+\frac{1}{99.100}\)

\(=1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+...+\frac{1}{99}-\frac{1}{100}\)

\(=1-\frac{1}{100}\)

\(=\frac{99}{100}\)

b)\(\frac{5}{11.16}+\frac{5}{16.21}+...+\frac{5}{61.66}\)

\(=\frac{1}{11}-\frac{1}{16}+\frac{1}{16}-\frac{1}{21}+....+\frac{1}{61}-\frac{1}{66}\)

\(=\frac{1}{11}-\frac{1}{66}\)

\(=\frac{5}{66}\)

a,\(\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{98.99}+\frac{1}{99.100}\)

ta có:

\(\frac{1}{1.2}=\frac{2-1}{1.2}=\frac{2}{1.2}-\frac{1}{1.2}=1-\frac{1}{2}\)

\(\frac{1}{2.3}=\frac{3-2}{2.3}=\frac{3}{2.3}-\frac{2}{2.3}=\frac{1}{2}-\frac{1}{3}\)

...

\(\frac{1}{99.100}=\frac{1}{99}-\frac{1}{100}\)

= \(1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+...+\frac{1}{99}-\frac{1}{100}\)

=\(1-\frac{1}{100}=\frac{99}{100}\)

b,

\(\frac{5}{11.16}+\frac{5}{16.21}+\frac{5}{21.16}+...+\frac{5}{61.66}\)

ta có:

\(\frac{5}{11.16}=\frac{16-11}{11.16}=\frac{16}{11.16}-\frac{11}{11.16}=\frac{1}{11}-\frac{1}{16}\)

\(\frac{5}{16.21}=\frac{21-16}{16.21}=\frac{21}{16.21}-\frac{16}{16.21}=\frac{1}{16}-\frac{1}{21}\)

...

\(\frac{5}{61.66}=\frac{66-61}{61.66}=\frac{66}{61.66}-\frac{61}{61.66}=\frac{1}{61}-\frac{1}{66}\)

= \(\frac{1}{11}-\frac{1}{16}+\frac{1}{16}-\frac{1}{21}+...+\frac{1}{61}-\frac{1}{66}\)

=\(\frac{1}{11}-\frac{1}{66}\)=\(\frac{5}{66}\)

1. \(\frac{-17}{21}:\left(\frac{5}{4}-\frac{2}{5}\right)< x+\frac{4}{7}< 1-\frac{1}{2}+\frac{1}{3}-\frac{1}{4}\)

\(-\frac{17}{21}:\frac{17}{20}< x+\frac{4}{7}< \frac{7}{12}\)

\(-\frac{20}{21}< x+\frac{4}{7}< \frac{7}{12}\)

\(-\frac{80}{84}< \frac{84x+48}{84}< \frac{49}{84}\)

\(-80< 84x+48< 49\)

\(\begin{cases}-80< 84x+48\\84x+48< 49\end{cases}\) 

\(\begin{cases}84x>-128\\84x< 1\end{cases}\)

\(\begin{cases}x>-\frac{32}{21}\\x< \frac{1}{84}\end{cases}\)

\(\Rightarrow-\frac{32}{21}< x< \frac{1}{84}\)

\(-\frac{17}{21}\div\left(\frac{5}{4}-\frac{2}{5}\right)< x+\frac{4}{7}< 1-\frac{1}{2}+\frac{1}{3}-\frac{1}{4}\)

\(-\frac{20}{21}< x+\frac{4}{7}< \frac{7}{12}\)

\(-\frac{32}{21}< x< \frac{1}{84}\)

\(-1^{11}_{21}< x< \frac{1}{84}\)

\(\Rightarrow x\in\left\{-1;0\right\}\)

Vậy x = 0

\(\frac{4}{3}\times1,25\times\left(\frac{16}{5}-\frac{5}{16}\right)< 2x< 4-\frac{4}{3}+3-\frac{3}{2}+2\)

\(\frac{77}{16}< 2x< \frac{37}{6}\)

\(\frac{77}{32}< x< \frac{37}{12}\)

\(2^{13}_{32}< x< 3^1_{12}\)

=> x = 3

2. \(\frac{4}{3}.1,25\left(\frac{16}{5}-\frac{5}{16}\right)< 2x< 4-\frac{4}{3}+3-\frac{3}{2}+2\)

\(\frac{16}{15}.\frac{231}{80}< 2x< \frac{37}{6}\)

\(\frac{77}{25}< 2x< \frac{37}{6}\)

\(\begin{cases}\frac{77}{25}< 2x\\2x< \frac{37}{6}\end{cases}\)

\(\begin{cases}2x>\frac{77}{25}\\x< \frac{37}{12}\end{cases}\)

\(\begin{cases}x>\frac{77}{50}\\x< \frac{37}{12}\end{cases}\)

\(\frac{77}{50}< x< \frac{37}{12}\)

a) 1 + 1/4 + 1/8 + 1/16

= 16/16 + 4/16 + 2/16 + 1/16

= 23/16

b) 2 - 1/8 - 1/12 - 1/16

= 96/48 - 6/46 - 4/48 - 3/48

= 83/48

c) 4/99 × 18/5 : 12/11 + 3/5

= 8/55 : 12/11 + 3/5

= 2/15 + 3/5

= 2/15 + 9/15

= 11/15

d) (1 - 3/4) × (1 + 1/3) : (1 - 1/3)

= 1/4 × 4/3 : 2/3

= 1/3 : 2/3

= 2

1 + 1/4 + 1/8 + 1/16

= 16 + 4 + 2 + 1 / 16

=23/16

2-1/8-1/12-1/16

= 96 - 6 - 4 - 3 / 48

= 83 / 48

4/99 x 18/5 : 12 /11 + 3/5

= 4/99 x 18/5 x 11/12 + 3/5

= 2/15 + 3/5

= 11/15

(1 - 3/4) x (1+1/3) : (1-1/3) 

= 1/4 x 4/3 : 2/3

= 1/4 x 4/3 x 3/2

= 1/2

c: \(=\dfrac{3}{2}\cdot1-1-20=\dfrac{3}{2}-21=\dfrac{-39}{2}\)