= 12,5 x 2 + 15 x 4 + 3 x 5

= 25 + 60 + 15 = 100

100

Trả lời :

858 : 26 = 33

6816 : 32 = 213

@Duy

#Vuaminhthaito 

~Hok tốt~

!!!!!!

858 : 26 = 33

6816 : 32 = 213

ko có ai giải chi tiết đc à, hả?

số nước cần phải đổ vào bể để bể đầy là

\(1-\frac{3}{4}=\frac{1}{4}\)(bể)

khi mở vòi nước thì số thời gian bể sẽ đầy là \(\frac{1}{4}:\frac{1}{8}=2\)(giờ)

vậy....

12.5* gọi hai số đó là a và b

ta có:a-b=9 (1)

\(\frac{7}{9}a=\frac{28}{33}b\)

=> \(a=\frac{28}{33}b:\frac{7}{9}\)

\(=>a=\frac{12}{11}b\)(2)

thay (2) vào (1) ta đc

\(\frac{12}{11}b-b=9\)

=> \(\frac{1}{11}b=9\)

=>b=99

=> a=99+9=108

vậy...

ta có: 1/1.2 - 1/2.3 = 3 - 1/1.2.3 = 2/1.2.3;

         1/2.3 - 1/3.4 = 4 - 2/2.3.4 = 2/2.3.4;....

    => 1/1.2.3 = 1/2 ( 1/1.2 - 1/2.3);

          1/2.3.4 = 1/2.(1/2.3 - 1/3.4);...

do đó: M = 1/2 ( 1/1.2 - 1/2.3 + 1/2.3 - 1/3.4 +..............+ 1/10.11 - 1/11.12

              = 1/2.( 1/2 - 1/11.12)

              = 1/2.(1/2 - 1/1/11.12)

              = 1/2.65/132

               = 65/264

tk đi nhé đúng 100% lun

Ta có: M = 1/1.2.3 + 1/2.3.4 + 1/3.4.5 + ... + 1/10.11.12

              = 1/2.(1/1.2 - 1/2.3) + 1/2.(1.2.3 - 1/3.4) + 1/2.(1/3.4 - 1/4.5) + ... + 1/2.(1/10.11 - 1/11.12)

              = 1/2.(1/1.2 - 1/2.3 + 1/2.3 - 1/3.4 + 1/3.4 - 1/4.5 + ... + 1/10.11 - 1/11.12)

              = 1/2.(1/1.2 - 1/11.12) = 1/2.(1/2 - 1/132) = 1/2 . 65/132 = 65/264

k mình nha

** Bổ sung điều kiện $x,y$ nguyên. 

Lời giải:

$x(y-2)+y=7$

$\Rightarrow x(y-2)+(y-2)=5$

$\Rightarrow (x+1)(y-2)=5$

Do $x,y$ nguyên nên $x+1, y-2$ cũng nguyên. Ta có các TH sau:

TH1: $x+1=1, y-2=5$

$\Rightarrow x=0, y=7$ (tm) 

TH2: $x+1=-1, y-2=-5$

$\Rightarrow x=-2; y=-3$ (tm)

TH3: $x+1=5, y-2=1$

$\Rightarrow x=4; y=3$ (tm) 

TH4: $x+1=-5; y-2=-1$
$\Rightarrow x=-6; y=1$ (tm)

=> X=201-95

=>X=106

\(x=201-\left(15+27+53\right)\)

\(\Leftrightarrow x=201-95\)

\(\Leftrightarrow x=106\)

Vậy x = 106

\(x=201-\left(15+27+53\right)\)

\(x=201-\left(42+53\right)\)

\(x=201-95\)

\(x=106\)

# Kukad'z Lee'z

Bài 1: 

a: Sai

b: Sai

\(A=\frac{9}{1.2}+\frac{9}{2.3}+\frac{9}{3.4}+...+\frac{9}{2019.2020}\)

\(=9\left(\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{2019.2020}\right)\)

\(=9\left(1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{2019}-\frac{1}{2020}\right)\)

\(=9\left(1-\frac{1}{2020}\right)\)

\(=9.\frac{2019}{2020}\)

\(=\frac{18171}{2020}\)

\(A=\frac{9}{1.2}+\frac{9}{2.3}+\frac{9}{3.4}+...+\frac{9}{2019.2020}\)

\(A=9.\left(\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{2019.2020}\right)\)

\(A=9\left(\frac{1}{1}-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{2019}-\frac{1}{2020}\right)\)

\(A=9\left(1-\frac{1}{2020}\right)=\frac{9.2019}{2020}=\frac{18171}{2020}\)

...

\(A=\frac{9}{1.2}+\frac{9}{2.3}+\frac{9}{3.4}+...+\frac{9}{2019.2020}\)

\(A=9\left(\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{2019.2020}\right)\)

\(A=9\left(\frac{1}{1}-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{2019}-\frac{1}{2020}\right)\)

\(A=9.\left(1-\frac{1}{2020}\right)\)

\(A=9.\left(\frac{2020}{2020}-\frac{1}{2020}\right)\)

\(A=9.\frac{2019}{2020}\)

\(A=\frac{18171}{2020}\)

hok tốt!