-6,35 x 0,25 - 6,35 x 1,75 + 6,35

= - 6,35 x (0,25 + 1,75 - 1)

= -6,35 x (2 - 1)

= -6,35 x 1

= - 6,35

\(-6,35\cdot0,25-6,35\cdot1,75+6,35\)

\(=6,35\left(-0,25-1,75+1\right)\)

\(=6,35\cdot\left(-2+1\right)\)

\(=6,35\cdot\left(-1\right)=-6,35\)

\(\dfrac{x-1}{2023}-\dfrac{1}{10}-\dfrac{1}{15}-\dfrac{1}{21}-...-\dfrac{1}{120}=\dfrac{5}{8}\)

=>\(\dfrac{x-1}{2023}-\left(\dfrac{1}{10}+\dfrac{1}{15}+...+\dfrac{1}{120}\right)=\dfrac{5}{8}\)

=>\(\dfrac{x-1}{2023}-2\left(\dfrac{1}{20}+\dfrac{1}{30}+...+\dfrac{1}{240}\right)=\dfrac{5}{8}\)

=>\(\dfrac{x-1}{2023}-2\left(\dfrac{1}{4}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{6}+...+\dfrac{1}{15}-\dfrac{1}{16}\right)=\dfrac{5}{8}\)

=>\(\dfrac{x-1}{2023}-2\left(\dfrac{1}{4}-\dfrac{1}{16}\right)=\dfrac{5}{8}\)

=>\(\dfrac{x-1}{2023}-2\cdot\dfrac{3}{16}=\dfrac{5}{8}\)

=>\(\dfrac{x-1}{2023}=\dfrac{5}{8}+\dfrac{3}{8}=\dfrac{8}{8}=1\)

=>x-1=2023

=>x=2024

-16 x (-0,125) x (-0,5)

= 2 x (-0,5)

= - 1

=-1 nha

\(\frac{2}{3n}=\frac{6}{3\left(n+4\right)}\)

\(\Rightarrow\frac{2.3}{3.3n}=\frac{6}{3\left(n+4\right)}\)

\(\Rightarrow9n=3n+12\)

\(\Rightarrow6n=12\)

\(\Rightarrow n=12:6\)

\(\Rightarrow n=2\)

Còn cách # :)

\(\frac{2}{3n}=\frac{6}{3\left(n+4\right)}\)

\(\Leftrightarrow\frac{2}{3n}=\frac{2}{n+4}\)

<=> 2(n + 4) = 3n.2

<=> 2(n + 4) = 6n

<=> 2n + 8 = 6n

<=> 2n = 6n - 8

<=> 2n - 6n = 6n - 8 - 6n

<=> -4n = -8

<=> n = (-8) : (-4)

<=> n = 2

=> n = 2

 A = 1.2 + 2.3 + 3.4 + ... + 2013.2014 
3A = 1.2.3 + 2.3.3 + 3.4.3 + ... + 2013.2014.3 
Mà : 
1.2.3 = 1.2.3 
2.3.3 = 2.3.4 - 2.3.1 
3.4.3 = 3.4.5 - 3.4.2 

2012.2013.3 = 2012.2013.2014 - 2012.2013.2011 
2013.2014.3 = 2013.2014.2015 - 2013.2014.2012 
Cộng tất cả, vế theo vế ---> 3S = 2013.2014.2015 
---> A = 2013.2014.2015 / 3 = 2723058910.

của bạn đây

A = \(\frac13\) + \(\frac16\) + \(\frac{1}{10}\) + \(\frac{1}{15}\) + ... + \(\frac{1}{45}\)

A = \(\frac26\) + \(\frac{2}{12}\) + \(\frac{2}{20}\) + \(\frac{2}{30}\) + ... + \(\frac{2}{90}\)

A = 2.(\(\frac{1}{2.3}\) + \(\frac{1}{3.4}\) + \(\frac{1}{4.5}\) + ... + \(\frac{1}{9.10}\))

A = 2.(\(\frac12-\frac13\) + \(\frac13-\frac14\) +\(\frac14-\) \(\frac15\) + ... + \(\frac19\) - \(\frac{1}{10}\))

A = 2.(\(\frac12-\frac{1}{10}\))

A = 2.\(\frac25\)

A = \(\frac45\)

\(\dfrac{7}{12}-\dfrac{9}{20}=\dfrac{35}{60}-\dfrac{27}{60}=\dfrac{8}{60}=\dfrac{2}{15}\)

\(167\times89-167\times35+54\times833\)

\(=167\times\left(89-35\right)+54\times833\)

\(=167\times54+54\times833\)

\(=54\times\left(167+833\right)\)

\(=54\times1000\)

\(=54000\)

\(876\times32+56\times124+24\times876\)

\(=876\times\left(32+24\right)+56\times124\)

\(=876\times56+56\times124\)

\(=56\times\left(876+124\right)\)

\(=56\times1000\)

\(=56000\)

\(A=2+5+8+11+...+146+149\)

\(A=\left(149+2\right)\times\left[\left(149-2\right)\div3+1\right]\div2\)

\(A=151\times50\div2\)

\(A=3775\)

\(5394\times768-1394\times769+5394\)

\(=5394\times\left(768+1\right)-1394\times769\)

\(=5394\times769-1394\times769\)

\(=\left(5394-1394\right)\times769\)

\(=4000\times769\)

\(=3076000\)

Sửa đề 

\(2013\times7645+2014\times2355-2355\)

\(=2013\times7645+2355\times\left(2014-1\right)\)

\(=2013\times7645+2355\times2013\)

\(=2013\times\left(7645+2355\right)\)

\(=2013\times10000\)

\(=20130000\)

\(B=1+4+7+10+...+61+64\)

\(B=\left(64+1\right)\times\left[\left(64-1\right)\div3+1\right]\div2\)

\(B=65\times22\div2\)

\(B=715\)

Học tốt 

Lời giải:

20 trang còn lại ứng với số phần cuốn sách là:

$1-\frac{2}{5}-\frac{7}{15}=\frac{2}{15}$ 

Số trang sách của cuốn sách là: $20: \frac{2}{15}=150$ (trang)

Ngày thứ ba anh đọc được, số phần trang sách là:

1-2/5-7/15=2/15( trang)

Cuốn sách đó có số trang là

20: 2/15 =150 (trang)

Đ/S:150 trang

\(x>9,99\) nên \(x\in\left\{10,11,12,...\right\}\)

Mà x bé nhất nên \(x=10\)

10,00000000000..1