125 x 98 + 125 x 46-52 x 25

125 x (98+46)  - 52 x 25

125 x 144 -52 x25

18000 -1300

=16700

=

a, 27 x 39 + 27 x 63 - 2 x 27

= 27 x ( 39 + 63 - 2 )

= 27 x 100

= 2700

b, 128 x 46 + 128 x 32 + 128x 22

= 128 x ( 46 + 32 + 22 )

= 128 x 100

= 12800

c, 12 x 35 + 35 x 182 - 35 x 94

= 35 x ( 12 + 182 - 94 )

= 35 x 100

= 3500

d, 456 : 2 x 18 + 456 : 3 - 102

= 228 x 18 + 152 - 102

= 4104 + 50

= 4154

\(\text{a, 27 x 39 + 27 x 63-2 x 27 =27 x (39+63-2) = 27 x 100 =2700}\)

\(\text{b, 128 x 46 +128 x 32 +128 x 22 =128 x (46+32+22)=128 x 100=12800}\)

\(\text{c , 12 x 35 +35 x 182 -35 x 94 =35 x (12+182-94)=35 x 100=3500.}\)

\(\text{d, 456:2 x 18 +456 :3 -102 =4140+152-102=4190}\)

2, 

\(45-\left(x+9\right)=6\Rightarrow45-x-9-6\Rightarrow36-x=6\Rightarrow x=30\)

\(x+7-25=13\Rightarrow x-18=13\Rightarrow x=31\)

\(450:\left(x-19\right)=50\Rightarrow x-19=9\Rightarrow x=28\)

\(4\times\left(x+41\right)=400\Rightarrow x+41=100\Rightarrow x=59\)

\(x+73-26=76\Rightarrow x+47=76\Rightarrow x=31\)

​

c)

\(\left(1-\frac{1}{2}\right)+\left(1-\frac{1}{6}\right)+....+\left(1-\frac{1}{42}\right)+\left(1-\frac{1}{56}\right)\)

\(\left(1+1+1+....+1+1\right)+\left(\frac{1}{1\times2}+\frac{1}{2\times3}+...+\frac{1}{6\times7}+\frac{1}{7\times8}\right)\)(Có  7 số 1)

\(7+1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+....+\frac{1}{6}-\frac{1}{7}+\frac{1}{7}-\frac{1}{8}\)

\(7+1-\frac{1}{8}=\frac{63}{8}\)

Gợi ý 1 bài c) còn d) e) cũng làm như vậy nhé

Chúc bạn học tốt !!!

a,48x19+48x115+124x52

=48x(19+115)+124x52

=48x124+124x52

=124x(48+52)

=124x100

=12400

b,27x121-87x27+73x34

=27x(121-87)+73x34

=27x34+73x34

=34x(27+73)

=34x100

=3400

c,125x98-125x46-52x25

=125x(98-46)-52x25

=125x52-52x25

=52x(125-25)

=52x100

=5200

d,136x23+136x17-40x36

=136x(23+17)-40x36

=136x40-40x36

=40x(136-36)

=40x100

=4000

e,17x93+116x83+17x23

=17x93+17x23+116x83

=17x(93+23)+116x83

=17x116+116x83

=116x(17+83)

=116x100

=11600

g,19x27+47x81+19x20

=19x27+19x20+47x81

=19x(27+20)+47x81

=19x47+47x81

=47x(19+81)

=47x100

=4700

h,87x23+13x93+70x87

=87x23+70x87+13x93

=87x(23+70)+13x93

=87x93+13x93

=93x(87+13)

=93x100

=9300

Nhớ like mik nhé!^-^ Mất bao thời gian của mik đấy!

Sửa đề : \(\frac{1}{2}+\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+...+\frac{1}{x\left(x+1\right)}=\frac{98}{100}\)

\(\Leftrightarrow\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+\frac{1}{4.5}+...+\frac{1}{x\left(x+1\right)}=\frac{98}{100}\)

\(\Leftrightarrow\frac{2-1}{1\times2}+\frac{3-2}{2\times3}+\frac{4-3}{3\times4}+\frac{5-4}{4\times5}+....+\frac{\left(x+1\right)-x}{x\left(x+1\right)}=\frac{98}{100}\)

\(\Leftrightarrow\frac{1}{1}-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+....+\frac{1}{x}-\frac{1}{\left(x+1\right)}=\frac{98}{100}\)

\(\Leftrightarrow\frac{1}{1}-\frac{1}{\left(x+1\right)}=\frac{98}{100}\)

\(\Leftrightarrow\frac{1}{\left(x+1\right)}=\frac{1}{1}-\frac{98}{100}\)

\(\Leftrightarrow\frac{1}{\left(x+1\right)}=\frac{1}{50}\)

\(\Leftrightarrow x=50-1=49\)

Sửa đề: \(\frac{1}{2}+\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+...+\frac{1}{x\left(x+1\right)}=\frac{98}{100}\)

(=) \(\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+\frac{1}{4.5}+...+\frac{1}{x\left(x+1\right)}=\frac{98}{100}\)

(=)\(1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+...+\frac{1}{x}-\frac{1}{x+1}=\frac{98}{100}\)

(=)\(1-\frac{1}{x+1}=\frac{98}{100}\)

(=)\(\frac{1}{x+1}=1-\frac{98}{100}\)

(=)\(\frac{1}{x+1}=\frac{1}{50}\)=> \(x+1=50\)

                                    \(x=50-1\)

                                    \(x=49\)

T_i_c_k cho mình nha,thanks you so much!

\(\dfrac{1}{2}+\dfrac{1}{6}+\dfrac{1}{12}+\dfrac{1}{20}+...+\dfrac{1}{110}\)

\(=\dfrac{1}{1\times2}+\dfrac{1}{2\times3}+\dfrac{1}{3\times4}+\dfrac{1}{4\times5}+...+\dfrac{1}{10\times11}\)

= 1 - \(\dfrac{1}{2}+\dfrac{1}{2}-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{4}+\dfrac{1}{4}-\dfrac{1}{5}+...+\dfrac{1}{10}-\dfrac{1}{11}\)

= \(1-\dfrac{1}{11}=\dfrac{10}{11}\)

\(\dfrac{1}{1.2}+\dfrac{1}{2.3}+\dfrac{1}{3.4}+\dfrac{1}{4.5}+...+\dfrac{1}{10.11}=1-\dfrac{1}{2}+\dfrac{1}{2}-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{4}+\dfrac{1}{4}-\dfrac{1}{5}+...+\dfrac{1}{10}-\dfrac{1}{11}=1-\dfrac{1}{11}=\dfrac{10}{11}\)

A= 1/2 + 1/6 + 1/12 + 1/20 + 1/30 + 1/42 + 1/56 + 1/72 + 1/90 

=1/(1.2)+1/(2.3)+1/(3.4)+1/(4.5) +1/(5.6)+1/(6.7)+1/(7.8) +1/(8.9)+1/(9.10) 

=1-1/2+1/2-1/3+1/3-1/4+1/4-1/5.+1/5-1/6... +1/9-1/10 

=1-1/10 

=9/10

Me too ! 

\(\frac{1}{2}+\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+\frac{1}{30}+\frac{1}{42}+\frac{1}{56}+\frac{1}{72}+\frac{1}{90}=x-\left(2+4+..+100\right)\)

Gọi \(\frac{1}{2}+\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+\frac{1}{30}+\frac{1}{42}+\frac{1}{56}+\frac{1}{72}+\frac{1}{90}\)là \(A\)

         \(\left(2+4+...+100\right)\)là \(B\). Ta có :  

\(A=\frac{1}{1\cdot2}+\frac{1}{2\cdot3}+\frac{1}{3\cdot4}+\frac{1}{4\cdot5}+\frac{1}{5\cdot6}+\frac{1}{6\cdot7}+\frac{1}{7\cdot8}+\frac{1}{8\cdot9}+\frac{1}{9\cdot10}\)

\(A=\frac{1}{1}-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+....+\frac{1}{9}-\frac{1}{10}\)

\(A=\frac{1}{1}-\frac{1}{10}=\frac{9}{10}\)

Số số hạng của \(B\)là: \(\left(100-2\right)\div2+1=50\)

Tổng của \(B\)là: \(\left(2+100\right)\times50\div2=2550\)

\(\Rightarrow\frac{1}{2}+\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+...+\frac{1}{90}=x-\left(2+4+..+100\right)=\frac{9}{10}=x-2550\)

\(\Rightarrow x=2550+\frac{9}{10}=2550+0,9=2550,9\)

D=1/2+1/6+1/12+...+1/90+1/100

D=(1/1x2+1/2x3+...+1/9x10)+1/100

D=(1-1/2+1/2-1/3+....+1/9-1/10)+1/100

D=(1-1/10)+1/100

D=9/10+1/100

D=91/100

D=1/2+1/6+1/12+...+1/90+1/100

D=(1/1x2+1/2x3+...+1/9x10)+1/100

D=(1-1/2+1/2-1/3+....+1/9-1/10)+1/100

D=(1-1/10)+1/100

D=9/10+1/100

D=91/100

Đặt D = \(\frac{1}{2}+\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+..+\frac{1}{100}\)

\(=1-\frac{1}{2}+\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+...+\frac{1}{100}\)

\(=1-\frac{1}{100}\)

\(=\frac{99}{100}\)

Đặt D = \(\frac{1}{2}+\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+...+\frac{1}{100}\)

\(=1-\left(\frac{1}{2}+\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+...+\frac{1}{100}\right)\)

\(=1-\frac{1}{100}\)

\(=\frac{99}{100}\)

và k cho ai làm đúng