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30+29+28+.......+2+1=(1+2+3+4+5).x
(30+1)x30:2=15.x
465=15.x
x=465:15
x=31
~shizadon~
Theo bài ra ta có:
30 + 29 + 28 + ... + 2 + 1 = (1 + 2 + 3 + 4 + 5) . x
(30 + 1) x 30 : 2 = 15 . x
x = 465 : 15
x = 31
![](https://rs.olm.vn/images/avt/0.png?1311)
a)15/16:3/8x3/4
=15/16:6/16x12/16
=15/16x16/6x12/16
=15/6x12/16
=30/16=15/8
b)5/11x18/29-5/11x8/29+5/11x19/29
=5/11x(18/29-8/29+19/29)
=5/11x1=5/11
![](https://rs.olm.vn/images/avt/0.png?1311)
a)\(\frac{2}{7}\)= \(\frac{4}{14}\)= \(\frac{6}{21}\)=\(\frac{8}{28}\)= ...
vì 5 < y < 29 \(\Rightarrow\)\(\frac{x}{y}\)= \(\frac{4}{14}\)= \(\frac{6}{21}\)= \(\frac{8}{28}\)
b)\(\frac{28}{8}\)= \(\frac{7}{2}\)= \(\frac{14}{4}\)= \(\frac{21}{6}\)= \(\frac{35}{10}\)= ...
vì 1 < y < 10\(\Rightarrow\)\(\frac{x}{y}\)= \(\frac{14}{4}\)= \(\frac{21}{6}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(\dfrac{4}{5}x-x-\dfrac{3}{2}x+\dfrac{4}{3}=\dfrac{1}{2}-\dfrac{6}{5}\\ \Rightarrow\left(\dfrac{4}{5}-1-\dfrac{3}{2}\right)x=-\dfrac{7}{10}-\dfrac{4}{3}\\ \Rightarrow-\dfrac{17}{10}x=\dfrac{-61}{30}\\ \Rightarrow x=\dfrac{61}{51}\)
\(\Leftrightarrow x\cdot\dfrac{-17}{10}=\dfrac{1}{2}-\dfrac{6}{5}-\dfrac{4}{3}=\dfrac{-61}{30}\)
hay x=61/51
Ta có
30 + 29 + 28 + 27 + ... + 2 + 1 = (1 + 2 + 3 + 4 + 5).x
(30.31):2 = 15.x
465 = 15x
x = 465 : 15
x = 31
Vậy x = 31 là giá trị cần tìm
Theo bài ra ta có:
30 + 29 + 28 + ... + 2 + 1 = (1 + 2 + 3 + 4 + 5) . x
(30 + 1) x 30 : 2 = 15 . x
x = 465 : 15
x = 31