a) \(\frac{5}{6}+\frac{11}{12}+\frac{19}{20}+...+\frac{89}{90}\)

\(=1-\frac{1}{6}+1-\frac{1}{12}+...+1-\frac{1}{90}\)

\(=\left(1+1+1+...+1\right)-\left(\frac{1}{6}+\frac{1}{12}+...+\frac{1}{90}\right)\)

\(=\left(1+1+1+...+1\right)-\left(\frac{1}{2\cdot3}+\frac{1}{3\cdot4}+...+\frac{1}{9\cdot10}\right)\)

Từ 2 đến 9 có : ( 9 - 2 ) / 1 + 1 = 8 ( số hạng ) => có 8 số 1

\(\Rightarrow8-\left(\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{9}-\frac{1}{10}\right)\)

\(=8-\left(\frac{1}{2}-\frac{1}{10}\right)\)

\(=8-\frac{2}{5}=\frac{38}{5}\)

b) \(\frac{1}{2}+\frac{5}{6}+\frac{11}{12}+...+\frac{109}{110}\)

\(=1-\frac{1}{2}+1-\frac{1}{6}+...+1-\frac{1}{110}\)

\(=\left(1+1+1+...+1\right)-\left(\frac{1}{2}+\frac{1}{6}+...+\frac{1}{110}\right)\)

\(=\left(1+1+...+1\right)-\left(\frac{1}{1\cdot2}+\frac{1}{2\cdot3}+...+\frac{1}{10\cdot11}\right)\)

Từ 1 đến 10 có : ( 10 - 1 ) / 1 + 1 = 10 ( số hạng ) => có 10 số 1

\(\Rightarrow10-\left(1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+...+\frac{1}{10}-\frac{1}{11}\right)\)

\(=10-\left(1-\frac{1}{11}\right)\)

\(=10-\frac{10}{11}=\frac{100}{11}\)

100/11 nha

câu b bằng 891/110

câu a bằng 76/10

24 . 25 + ( 4 . 6 ) . 37 + 24 . 38

24 . 25 + 24 . 37 + 24 . 38

24 . ( 25 + 37 + 38 )

24 . 100 

2400

24 . 25 + 4 . 37 . 6 +24 . 38

= 24 . 25 + 24 . 37 + 24 . 38

= 24 . ( 25 + 38 + 37 )  

= 24 . 100 = 2400

5, 31+1240++1829=3100

6. -19+836+1829=2646

7.  54.43-32.35=2322-1120=1202

8 2018(31+16+50)=2018.97=195746

9. 16(34-21+55)=16.68=1088

10. 63(29-31-98)=63.(-100)=-6300

cả lời giải thì

mới được

bạn ạ

81/10

81/10

mình nha

a ) 10 nha 

b ) 41 ( không chắc lắm )

c ) 10700

d ) 88

e) 454

Bài a,b tự làm:

c,99 x 2014-50 x 2014+2014

=(99-50+1) x 2014

=50 x 2014

=100700

d,(81 x 11):9

=891:9

=99

e,46 x 6+46 x 4

=46 x (4+6)

=46 x 10

=460

 1*2*3*4*5*6*7*8*9*10*11*12*13*14*15*16*17*18*19*0*20*21*22*23*24*25*26*27*28*29*30*31*32=0

=0 vì tích có thừa số 0 

0 vì số nào nhân 0 cũng bằng0

k mình nha !

44 x 19 + 19 x 55 + 19

= 44 x 19 + 19 x 55 + 19 x 1

= ( 44 + 55 + 1 ) x 19

=       100    x    19

=             1900

44 x 19 + 19 x 55 + 19

= 19 x (44+55)

= 19 x 99

= 1881

Hok tốt

k nha!

= 44 x 19 + 19 x 55 + 19 x 1

= ( 44 + 55 + 1 ) x 19

= 100 x 19

= 1900

81/10

ban viet loi giai ra cho mk voi

\(A=\frac{1}{2}+\frac{5}{6}+\frac{11}{12}+\frac{19}{20}+\frac{29}{30}+\frac{41}{42}+\frac{55}{56}+\frac{71}{72}+\frac{89}{90}\)

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

\(A=\left(1+1+...+1\right)-\left(\frac{1}{2}+\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+...+\frac{1}{72}+\frac{1}{90}\right)\) ( có 8 số 1)

\(A=9-\left(\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+\frac{1}{4.5}+...+\frac{1}{8.9}+\frac{1}{9.10}\right)\)

\(A=9-\left(1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+...+\frac{1}{8}-\frac{1}{9}+\frac{1}{9}-\frac{1}{10}\right)\)

\(A=9-\left(1-\frac{1}{10}\right)=9-1+\frac{1}{10}=8+\frac{1}{10}=8\frac{1}{10}\)