21.76+50.21-21.26
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14 tháng 10 2019
Bài 1: Tính(hợp lý nếu có thể)
a, \(21.76+50.21-21.26\)
\(=21\left(76+50-26\right)\)
\(=21.100\)
\(=2100\)
b, \(24.74+34.25+74\)
\(=74\left(24+1\right)+34.25\)
\(=74.25+34.25\)
\(=25\left(74+34\right)\)
\(=25.108\)
\(=2700\)
c, \(93.61+68.8-61\)
\(=61\left(93-1\right)+68.8\)
\(=61.92+544\)
\(=5612+544\)
\(=6156\)
d, \(13.75+25.13-140\)
\(=13\left(75+25\right)-140\)
\(=13.100-140\)
\(=1300-140\)
\(=1160\)
Bài 2: Tính.
a, \(2018-18:3^2\)
\(=2018-18:9\)
\(=2018-2\)
\(=2016\)
b, \(2.7^2+2019^0-81:3^3\)
\(=2.49+1-81:27\)
\(=98+1-3\)
\(=96\)
14 tháng 10 2019
Bài 1:
\(21\cdot76+50\cdot21-21\cdot26\\ =21\left(76+50-26\right)\\ =21\cdot100\\ =2100\)
\(34\cdot74+34\cdot25+74\\ =34\left(74+25\right)+74\\ =34\cdot99+74\\ =3366+74\\ =3440\)
\(93\cdot61+68\cdot8-61\\ =61\left(93-1\right)+544\\ =61\cdot92+544\\ =5612+544\\ =6156\)
\(13\cdot75+25\cdot13-140\\ =13\left(75+13\right)-140\\ =13\cdot88-140\\ =1144-140\\ =1004\)
Bài 2:
\(2018-18:3^2\\ =2018-18:9\\ =2018-2\\ =2016\)
\(2\cdot7^2+2019^0-81:3^3\\ =2\cdot49+1-81:27\\ =98+1-3\\ =99-3\\ =96\)
20 tháng 9 2023
Đặt:
\(A=\dfrac{7}{11\cdot16}+\dfrac{7}{16\cdot21}+\dfrac{7}{21\cdot26}+...+\dfrac{7}{61\cdot66}\)
\(\dfrac{5}{7}A=\dfrac{5}{11\cdot16}+\dfrac{5}{16\cdot21}+...+\dfrac{5}{61\cdot66}\)
\(\dfrac{5}{7}A=\dfrac{1}{11}-\dfrac{1}{16}+\dfrac{1}{16}-\dfrac{1}{21}+...+\dfrac{1}{61}-\dfrac{1}{66}\)
\(\dfrac{5}{7}A=\dfrac{1}{11}-\dfrac{1}{66}=\dfrac{6}{66}-\dfrac{1}{66}=\dfrac{5}{66}\)
\(A=\dfrac{5}{66}\cdot\dfrac{7}{5}=\dfrac{7}{66}\)
IE
3
12 tháng 7 2015
A=55/11.16+55/16.21+55/21.26+55/26.31+55/31.36+55/36.41
=11.(5/11.16+5/16.21+...+5/36.41)
=11.(1/11-1/16+1/16-1/21+...+1/36-1/41)
=11.(1/11-1/41)
=11.30/451
=30/41
6 tháng 4 2021
\(\dfrac{5x}{1.6}+\dfrac{5x}{6.11}+\dfrac{5x}{11.16}+\dfrac{5x}{16.21}+\dfrac{5x}{21.26}+\dfrac{5x}{26.31}=1\)
\(=x\left(\dfrac{5}{1.6}+\dfrac{5}{6.11}+\dfrac{5}{11.16}+\dfrac{5}{16.21}+\dfrac{5}{21.26}+\dfrac{5}{26.31}\right)=1\)
\(=x\left(1-\dfrac{1}{6}+\dfrac{1}{6}-\dfrac{1}{11}+\dfrac{1}{11}-\dfrac{1}{16}+\dfrac{1}{16}-\dfrac{1}{21}+\dfrac{1}{21}-\dfrac{1}{26}+\dfrac{1}{26}-\dfrac{1}{31}\right)=1\)
\(=x\left(1-\dfrac{1}{31}\right)=1\)
\(\Rightarrow x=1:\left(1-\dfrac{1}{31}\right)=\dfrac{31}{30}\)
NT
5
8 tháng 11 2019
\(A=\frac{5}{11.16}+\frac{5}{16.21}+...+\frac{5}{61.66}\)
\(=\frac{1}{11}-\frac{1}{16}+\frac{1}{16}-\frac{1}{21}+...+\frac{1}{61}-\frac{1}{66}\)
\(=\frac{1}{11}-\frac{1}{66}=\frac{5}{66}\)
8 tháng 11 2019
\(A=\frac{5}{11.16}+\frac{5}{16.21}+\frac{5}{21.26}+...+\frac{5}{61.66}\)
\(A=\frac{1}{11}-\frac{1}{16}+\frac{1}{16}-\frac{1}{21}+\frac{1}{21}-\frac{1}{26}+...+\frac{1}{61}-\frac{1}{66}\)
\(A=\frac{1}{11}-\frac{1}{66}\)
\(A=\frac{6}{66}-\frac{1}{66}\)
\(A=\frac{5}{66}\)
25 tháng 6 2020
TA CÓ :A=15-15/6+15/6-15/11+15/11-15/16+15/16-15/21+15/21-15/26+15/26-15/31+15/31-15/36
A=15-15/36=14,5833333 >2
25 tháng 6 2020
Làm
Ta có :
A = 15/1.6 + 15/6.11 + 15/11.16 + 15/16.21 + 15/21.26 + 15/26.31 + 15/31.36
A = 15. ( 1/1.6 + 1/6.11 + 1/11.16 + 1/16.21 + 1/21.26 + 1/26.31 + 1/31.36 )
A = 15 . ( 1/1 - 1/6 + 1/6 - 1/11 + 1/11-1/16 + 1/16 - 1/21 + 1/21 - 1/26 + 1/26 - 1/31 + 1/31 - 1/36 )
A = 15 . ( 1 - 1/36 )
A = 15 . ( 36 /36 - 1/36 )
A = 15 . 35/36
A = 175/12
Ta có : A = 175/12 với 2
Ta quy đồng :
+) A= 175/12 = 175.1/12.1 = 175/12
+) 2 = 2.12/1.12 = 24/12
Mà 175/12 > 24/12
=> 175/12 > 2
=> A > 2 ( đpcm )
HỌC TỐT
D
1
20 tháng 3 2017
E=\(\frac{10}{1\cdot6}\) +\(\frac{10}{6\cdot11}\) +\(\frac{10}{11\cdot16}\) +\(\frac{10}{16\cdot21}\) +\(\frac{10}{21\cdot26}\) +\(\frac{10}{26\cdot31}\) = 5*(1-\(\frac{1}{31}\) ) =5*\(\frac{30}{31}\) =\(\frac{150}{31}\)
21.76+50.21-21.26
=1596+1050-546
=2646-546
=2100
tk nhé