mình làm bài này rồi

chỉ mik cách để viết phân số r mik giải bài này cho

bài 6 \(\frac{2}{2\times4}+\frac{2}{4\times6}+\frac{2}{6\times8}+\ldots+\frac{2}{80\times82}+\frac{2}{82\times84}\)

= \(\frac12-\frac14+\frac14-\frac16+\frac16-\cdots+\frac{1}{80}-\frac{1}{82}+\frac{1}{82}-\frac{1}{84}\)

= \(\frac12-\left(\frac14-\frac14\right)-\left(\frac16-\frac16\right)-\cdots-\left(\frac{1}{82}-\frac{1}{82}\right)-\frac{1}{84}\)

=\(\frac12-0-0-\frac{1}{84}\)

=\(\frac12\) - \(\frac{1}{84}\)

=\(\frac{42}{84}-\frac{1}{84}\)

=\(\frac{41}{84}\)

Bài 7

a)\(\frac{19}{4}=4\frac34\)

b)\(\frac{27}{5}=5\frac25\)

c)\(\frac{56}{8}=7\frac08\)

\(1\frac{1}{3}:\left(1\frac{2}{3}-x\right)=\frac{8}{7}\)

\(\frac{4}{3}:\left(\frac{5}{3}-x\right)=\frac{8}{7}\)

\(\left(\frac{5}{3}-x\right)=\frac{4}{3}:\frac{8}{7}\)

\(\left(\frac{5}{3}-x\right)=\frac{7}{6}\)

\(x=\frac{5}{3}-\frac{7}{6}\)

\(x=\frac{1}{2}\)

Bài 2:

            theo thứ tự tăng dần:  \(\frac{75}{100};\)\(4\frac{1}{2};\)\(6,04;\)\(7.\)

\(1\frac{1}{3}:\left(1\frac{2}{3}-x\right)=\frac{8}{7}\Rightarrow\frac{4}{3}:\left(\frac{5}{3}-x\right)=\frac{8}{7}\)

\(\Rightarrow\frac{5}{3}-x=\frac{4}{3}:\frac{8}{7}\Rightarrow\frac{5}{3}-x=\frac{7}{6}\)

\(\Rightarrow x=\frac{5}{3}-\frac{7}{6}\Rightarrow x=\frac{1}{2}\)

\(a,2\frac{1}{18}+3\frac{5}{6}+1\frac{2}{3}\)

\(=2+\frac{1}{18}+3+\frac{5}{6}+1+\frac{2}{3}\)

\(=(2+3+1)+(\frac{1}{18}+\frac{5}{6}+\frac{2}{3})\)

\(=6+(\frac{1}{18}+\frac{15}{18}+\frac{12}{18})\)

\(=6+\frac{28}{18}\)

\(=6+\frac{14}{9}=7\frac{5}{9}=\frac{68}{9}\)

\(b,5\frac{3}{7}+(2\frac{5}{21}-1\frac{2}{3})\)

\(=5+\frac{3}{7}+2+\frac{5}{21}-1-\frac{2}{3}\)

\(=(5+2-1)+(\frac{3}{7}+\frac{5}{21}-\frac{2}{3})\)

\(=6+(\frac{9}{21}+\frac{5}{21}-\frac{14}{21})\)

\(=6+0=6\)

Chúc bạn học tốt

a) \(2\frac{1}{8}+3\frac{5}{6}+1\frac{2}{3}\)

\(=2\frac{3}{24}+3\frac{20}{24}+1\frac{16}{24}\)

\(=\left(2+3+1\right)+\frac{3+20+16}{24}\)

\(=6+\frac{13}{8}\)

\(=7\frac{5}{8}=\frac{61}{8}\)

b)\(5\frac{3}{7}+\left(2\frac{5}{21}-1\frac{2}{3}\right)\)

\(=5\frac{9}{21}+\left(2\frac{5}{21}-1\frac{14}{21}\right)\)

\(=5\frac{9}{21}+2\frac{5}{21}-1-\frac{14}{21}\)

\(=\left(5+2-1\right)+\frac{9+5-14}{21}\)

\(=6+0=6\)

a, 6/9+5/7+1/3=2/3+5/7+1/3=5/7+1=12/7

b, 17/7+6/5-20/14=17/7+6/5-10/7=6/5+1=11/5

c,2/5x1/4+3/4x2/5=2/5x(1/4+3/4)=2/5x1=2/5

d, 6/11:4/6+5/11:2/3=6/11:2/3+5/11:2/3=(6/11+5/11):2/3=3/2

nha

a)\(\frac{2}{3}+\frac{3}{4}+\frac{1}{6}=\frac{19}{12}\); b)\(2\frac{1}{10}-\frac{3}{4}-\frac{2}{5}=\frac{3}{4}\)c)\(\frac{1}{3}-\frac{1}{5}=\frac{2}{15}\)d) \(\frac{1}{5}-\frac{1}{7}=\frac{2}{35}\)