\(\frac{1}{10}+\frac{4}{20}+\frac{9}{30}+\frac{16}{40}+\frac{25}{50}\) \(+\frac{36}{60}+\frac{49}{70}+\frac{64}{80}+\frac{81}{90}\)

\(=\frac{1}{10}+\frac{1}{5}+\frac{3}{10}+\frac{2}{5}+\frac{1}{2}+\frac{3}{5}+\frac{7}{10}+\frac{4}{5}+\frac{9}{10}\)

\(=\left(\frac{1}{10}+\frac{9}{10}\right)+\left(\frac{1}{5}+\frac{4}{5}\right)+\left(\frac{3}{10}+\frac{7}{10}\right)+\left(\frac{2}{5}+\frac{3}{5}\right)+\frac{1}{2}\)

\(=1+1+1+1+0,5\)

\(=4+0,5\)

\(=4,5\)

1. b) (6/16+10/16)+(8/18+10/18)=16/16+18/18=1+1=2

a,(125*36):(5*9)=(125x40-125*4):45=(5000-500):45=4500:45=100

b,\(\frac{6}{16}+\frac{8}{18}+\frac{10}{16}+\frac{10}{18}\)\(=\left(\frac{6}{16}+\frac{10}{16}\right)+\left(\frac{8}{18}+\frac{10}{18}\right)\)\(=\frac{16}{16}+\frac{18}{18}=1+1=2\)

c,5,6*2+2,8*8+11,2*2-48,5=5,6*2+2,8*2*4+5,6*2*2-48,5=5,6*2+5,6*4+5,6*4-48,5

=5,6*(2+4+4)-48,5=5,6x10-48,4=56-48,5=7,5

cíu tôi với 

\(\frac{1}{10}+\frac{2}{20}+\frac{3}{30}+\frac{4}{40}+\frac{5}{50}+\frac{6}{60}+\frac{7}{70}+\frac{8}{80}+\frac{9}{90}\)

=\(\frac{1}{10}+\frac{1}{10}+\frac{1}{10}+\frac{1}{10}+\frac{1}{10}+\frac{1}{10}+\frac{1}{10}+\frac{1}{10}+\frac{1}{10}\)

=\(\frac{9}{10}\)

\(\frac{1}{10}+\frac{2}{20}+\frac{3}{30}+\frac{4}{40}+\frac{5}{50}+\frac{6}{60}+\frac{7}{70}+\frac{8}{80}+\frac{9}{90}=\frac{1}{10}+\frac{1}{10}+....+\frac{1}{10}=\frac{9}{10}\)

\(1-4+7-10+13-16+...+103-106+109\)

\(=\left(1+7+13+...+103+109\right)-\left(4+10+16+...+106\right)\)

\(=\left(\left(1+109\right)\times19:2\right)-\left(\left(106+4\right)\times18:2\right)\)

\(=1045-990\)

\(=55\)

Chúc bn học tốt!!!!!!

109+1=110

110:2=55

rút gọn mấy phân số trên thì còn

=1/10+1/10+1/10+1/10+1/10+1/10+1/10+1/10+1/10

=9x1/10

=9/10

\(\frac{1}{10}+\frac{2}{20}+\frac{3}{30}+\frac{4}{40}+\frac{5}{50}+\frac{6}{60}+\frac{7}{70}+\frac{8}{80}+\frac{9}{90}\)

\(=\frac{1}{10}+\frac{1}{10}+\frac{1}{10}+\frac{1}{10}+\frac{1}{10}+\frac{1}{10}+\frac{1}{10}+\frac{1}{10}+\frac{1}{10}\)

\(=\frac{1}{10}\times9\)

\(=\frac{9}{10}\)

A ) 4,7 x 4,5 - 4,7 x 4,4 

= 4,7 x ( 4,5 - 4,4 ) 

= 4,7 x 0,1 

= 0,47