tính nhanh: 3/17 + 1/22 + 5/3 - 22/17 + 14/17
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=\(\left(\dfrac{5}{17}+\dfrac{12}{17}\right)+\left(\dfrac{1}{22}-\dfrac{23}{22}\right)+\dfrac{2}{3}\)
=\(\dfrac{17}{17}-\dfrac{22}{22}+\dfrac{2}{3}\)
=\(1-1+\dfrac{2}{3}\)
=0+\(\dfrac{2}{3}\)
=\(\dfrac{2}{3}\)
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a) 5.2² - 18 : 3
= 5.4 - 18 : 9
= 20 - 2
= 18
b) 17 . 85 + 15 . 17 - 120
= 17 . (85 + 15) - 120
= 17 . 100 - 120
= 1700 - 120
= 1580
c) 2³ . 17 - 2³ . 14
= 8 . 17 - 8 . 14
= 8 . (17 - 14)
= 8 . 3
= 24
a) 5 . 22 – 18 : 32
= 5.4 – 18 : 9
= 20 – 2
= 18
b) 17 . 85 + 15 . 17 – 120
= 17. (85 + 15) – 120
= 17.100 – 120
= 170 – 120
= 50
c) 23 . 17 – 23 . 14
= 23.(17 - 14)
= 23.3
= 8.3
= 24
Tính nhanh
19 + 18 + 17 + 16 + 14 + 21 + 22 + 23 + 24 + 25 + 26
1/3 + 1/4 + 1/5 + 4/6 + 9/12 + 16/20
![](https://rs.olm.vn/images/avt/0.png?1311)
\(19+18+17+16+14+21+22+23+24+25+26\)
\(=\left(19+21\right)+\left(18+22\right)+\left(17+23\right)+\left(16+24\right)+\left(14+26\right)+25\)
\(=30+30+30+30+30+25\)
\(=175\)
\(\dfrac{1}{3}+\dfrac{1}{4}+\dfrac{1}{5}+\dfrac{4}{6}+\dfrac{9}{12}+\dfrac{16}{20}\)
\(=\dfrac{1}{3}+\dfrac{1}{4}+\dfrac{1}{5}+\dfrac{2}{3}+\dfrac{3}{4}+\dfrac{4}{5}\)
\(=\left(\dfrac{1}{3}+\dfrac{2}{3}\right)+\left(\dfrac{1}{4}+\dfrac{3}{4}\right)+\left(\dfrac{1}{5}+\dfrac{4}{5}\right)\)
\(\text{=}1+1+1\)
\(\text{=}3\)
![](https://rs.olm.vn/images/avt/0.png?1311)
a) \(\dfrac{\dfrac{3}{14}-\dfrac{3}{17}+\dfrac{3}{19}}{\dfrac{5}{19}+\dfrac{5}{14}-\dfrac{5}{17}}=\dfrac{3\left(\dfrac{1}{14}-\dfrac{1}{17}+\dfrac{1}{19}\right)}{5\left(\dfrac{1}{14}-\dfrac{1}{17}+\dfrac{1}{19}\right)}=\dfrac{3}{5}\)
c) \(\dfrac{\dfrac{2}{7}+\dfrac{2}{5}+\dfrac{2}{17}-\dfrac{2}{193}}{\dfrac{3}{7}+\dfrac{3}{5}+\dfrac{3}{17}-\dfrac{3}{293}}=\dfrac{2\left(\dfrac{1}{7}+\dfrac{1}{5}+\dfrac{1}{17}-\dfrac{1}{193}\right)}{3\left(\dfrac{1}{7}+\dfrac{1}{5}+\dfrac{1}{17}-\dfrac{1}{193}\right)}=\dfrac{2}{3}\)
d)
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a: \(=\dfrac{3}{22}\cdot22\cdot\dfrac{3}{11}=3\cdot\dfrac{3}{11}=\dfrac{9}{11}\)
b: \(=\dfrac{5}{6}\cdot\dfrac{2}{5}=\dfrac{1}{3}\)
c: =17/21(3/5+2/5)=17/21
![](https://rs.olm.vn/images/avt/0.png?1311)
a. ( 23 - 21) + ( 19 - 17) + ( 15 - 13) + ( 11 - 9) + ( 7 - 5) + ( 3 - 1)
= 2 + 2 + 2 + 2 + 2 + 2
= 2 x 6
= 12
b. ( 24 - 22 ) + ( 20 - 18 ) + ( 16 - 14 ) + ( 12 - 10) + ( 8 - 6 ) + ( 4 - 2)
= 2 + 2 + 2 + 2 + 2 + 2
= 2 x 6
= 12
![](https://rs.olm.vn/images/avt/0.png?1311)
a)5.4 – 18 : 9 b)17. (85 + 15) – 120
= 20 – 2 = 17.100 – 120
= 18 = 170 – 120
= 50
c)23.(17 - 14)
= 23.3
= 8.3
= 24
a) 5 . 2\(^2\) - 18 : 3
⇔ 5 . 4 - 18 : 3
⇔ 20 - 6
⇔ 14
b) 17 . 85 + 15 . 17 - 120
⇔ 17 . ( 85 + 15 ) - 120
⇔ 17 . 100 - 120
⇔ 1700 - 120
⇔ 1580
c) 2\(^3\) . 17 - \(2^3\) . 14
⇔ \(2^3\) . ( 17 - 14 )
\(\Leftrightarrow\) 8 . 3
⇔ 24
![](https://rs.olm.vn/images/avt/0.png?1311)
a) 2 + (-25) + 41+ (-2) + 25 +(-41)
= (-2 + 2) + (-25 + 25) + (-41 +41)
=0 + 0 + 0
=0
b) 10+ ( -17) +5 + (-7)+ 17 + (-15)
= (-15+10+5) + (-17+7) + 7
= 0 + 0 + 7
= 7
c)(-22) + (-14) + 17 + (-24) + 13+ 30
= [(-22) + (-14) + (-24)] + (17 + 13 + 30)
=-60 + 60
=0
a) 2 + (-25) + 41+ (-2) + 25 +(-41)
= (-2 + 2) + (-25 + 25) + (-41 +41)
=0 + 0 + 0
=0
![](https://rs.olm.vn/images/avt/0.png?1311)
a) 2 + (- 25) + 41 +(-2) +25 +(-41)= (-2 +2)+(-25+25)+(-41+41) = 0+0+0+0 = 0
b) 10 + (-17) + 5 + (-7) + 17+(-15) =(-17+17)+(10+5-15)+(-7) = 0+0-7 = -7
c) (-22) + (-14)+17 +(-24)+ 13 +30 = (-22 -14 -24) + ( 17 + 30 + 13 ) = -60 + 60 = 0
\(\dfrac{3}{17}+\dfrac{1}{22}+\dfrac{5}{3}-\dfrac{22}{17}+\dfrac{14}{17}\)
\(=\left(\dfrac{3}{17}+\dfrac{14}{17}-\dfrac{22}{17}\right)+\dfrac{113}{66}\)
\(=\dfrac{-5}{17}+\dfrac{113}{66}=\dfrac{-5\cdot66+113\cdot17}{17\cdot66}=\dfrac{1591}{1122}\)