tính giá trị biểu thức 5/8 + 3/8 : 2/3
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![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
Bài làm
\(M=\frac{3^2}{2.5}+\frac{3^2}{5.8}+\frac{3^2}{8.11}+...+\frac{3^2}{98.101}\)
\(M=3^2\left(\frac{1}{2}-\frac{1}{5}+\frac{1}{5}-\frac{1}{8}+\frac{1}{8}-\frac{1}{11}+...+\frac{1}{98}-\frac{1}{101}\right)\)
\(M=9\left(\frac{1}{2}-\frac{1}{101}\right)\)
\(M=9.\frac{101-2}{202}\)
\(M=9.\frac{99}{202}\)
\(M=\frac{891}{202}\)
Vậy \(M=\frac{891}{202}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(M=3\left(\frac{3}{2x5}+\frac{3}{5x8}+\frac{3}{8x11}+...+\frac{3}{98.101}\right).\)
\(M=3\left(\frac{5-2}{2.5}+\frac{8-5}{5.8}+\frac{11-8}{8.11}+...+\frac{101-98}{98.101}\right)\)
\(M=3\left(\frac{1}{2}-\frac{1}{5}+\frac{1}{5}-\frac{1}{8}+\frac{1}{8}-\frac{1}{11}+...+\frac{1}{98}-\frac{1}{101}\right)=3\left(\frac{1}{2}-\frac{1}{101}\right)=\frac{3.99}{202}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
10.213
11. 2 giờ 55 phút
12. 4 ngày 21 giờ
13.
a: 6,008
b: 4500
c: 5,628
d: 4,009
14.
a,8579 cm2
b,32,04 m2
c,187200m2
d,5,017 tấn
![](https://rs.olm.vn/images/avt/0.png?1311)
14:
a: \(85.79km^2=857900000000cm^2\)
b: \(32m^24dm^2=32.04m^2\)
c: \(1872dm^2=18.72m^2\)
d: 5 tấn 17kg=5,017 tấn
13:
a: \(6dm^38cm^3=6.008dm^3\)
b: \(4.5m^3=4500dm^3\)
c: \(5628dm^3=5.628m^3\)
d: \(4m^39dm^3=4.009m^3\)
12: =108h:3+80h
=36h+80h=116h
10:
3h18p+7h21p:3
=198p:441p:3
=198p+147p=345p
![](https://rs.olm.vn/images/avt/0.png?1311)
Lời giải:
a.
$\frac{5}{15}-\frac{1}{6}\times \frac{2}{5}=\frac{5}{15}-\frac{1}{15}=\frac{4}{15}$
b.
$\frac{8}{24}+\frac{3}{4}:\frac{1}{8}=\frac{1}{3}+6=\frac{19}{3}$
c.
$\frac{1}{7}: \frac{2}{8}-\frac{1}{7}=\frac{1}{7}\times 4-\frac{1}{7}$
$=\frac{1}{7}\times (4-1)=\frac{1}{7}\times 3=\frac{3}{7}$
![](https://rs.olm.vn/images/avt/0.png?1311)
\(=\dfrac{2}{3}\cdot\dfrac{6}{5}\cdot7+\dfrac{5}{6}\cdot\dfrac{1}{7}\cdot\dfrac{7}{8}\cdot3=\dfrac{28}{5}+\dfrac{5}{16}=\dfrac{473}{80}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(\dfrac{3}{8}+\dfrac{6}{15}:\dfrac{3}{5}\\ =\dfrac{3}{8}+\dfrac{2}{5}.\dfrac{5}{3}\\ =\dfrac{3}{8}+\dfrac{2}{3}\\ =\dfrac{9}{24}+\dfrac{16}{24}\\ =\dfrac{25}{24}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
Bài làm
\(M=\frac{3^2}{2.5}+\frac{3^2}{5.8}+\frac{3^2}{8.11}+...+\frac{3^2}{98.101}\)
\(M=3^2\left(\frac{1}{2.5}+\frac{1}{5.8}+\frac{1}{8.11}+...+\frac{1}{98.101}\right)\)
\(M=9.\left(\frac{1}{2}-\frac{1}{5}+\frac{1}{5}-\frac{1}{8}+\frac{1}{8}-\frac{1}{11}+...+\frac{1}{98}-\frac{1}{101}\right)\)
\(M=9\left(\frac{1}{2}-\frac{1}{101}\right)\)
\(M=9.\left(\frac{101}{202}-\frac{2}{202}\right)\)
\(M=9.\frac{99}{202}\)
\(M=\frac{891}{202}\)
Vậy \(M=\frac{891}{202}\)
M= 3.(3/2.5+ 3/5.8.....3/98.101)
= 3.( 1/2-1/5+1/5-1/8 +....+1/98-1/101)
=3.( 1/2-1/101)
= 3.( 101/202- 2/202)
=3. 99/202
= 297/202
Vậy M= 297/202 nha bạn
5/8 + 3/8 : 2/3 =
5/8 + 9/16 =
19/16
-.-
k mik
5/8+3/8:2/3=5/8+9/16=19/16