Question

Answer 1

Bài 4:

$S=\frac{4-1}{1.4}+\frac{7-4}{4.7}+\frac{10-7}{7.10}+\frac{13-10}{10.13}+\frac{16-13}{13.16}$

$=1-\frac{1}{4}+\frac{1}{4}-\frac{1}{7}+\frac{1}{7}-\frac{1}{10}+\frac{1}{10}-\frac{1}{13}+\frac{1}{13}-\frac{1}{16}$

$=1-\frac{1}{16}=\frac{15}{16}$

 

Answer 2

Bài 5:

a.

$x-\frac{1}{5}=\frac{7}{11}.\frac{3}{21}=\frac{1}{11}$

$x=\frac{1}{11}+\frac{1}{5}=\frac{16}{55}$

b.

$\frac{x}{25}=\frac{-3}{15}.\frac{7}{6}=\frac{-7}{30}$

$x=\frac{-7}{30}.25=\frac{-35}{6}$

c.

$x+\frac{7}{5}=\frac{9}{8}.\frac{4}{27}=\frac{1}{6}$

$x=\frac{1}{6}-\frac{7}{5}=\frac{-37}{30}$

d. $x:\frac{5}{11}=\frac{-4}{12}.6=-2$

$x=-2.\frac{5}{11}=\frac{-10}{11}$

 

 

Answer 3

Bài 6.

a/

$x-\frac{1}{2}=\frac{3}{10}.\frac{5}{6}=\frac{1}{4}$

$x=\frac{1}{4}+\frac{1}{2}=\frac{3}{4}$

b/

$\frac{x}{5}=\frac{-3}{14}.\frac{7}{3}=\frac{-1}{2}$

$x=\frac{-1}{2}.5=\frac{-5}{2}$
c/

$x+\frac{2}{3}=\frac{9}{15}.\frac{5}{27}=\frac{1}{9}$

$x=\frac{1}{9}-\frac{2}{3}=\frac{-5}{9}$

d.

$x:\frac{4}{11}=\frac{11}{4}.2=\frac{11}{2}$

$x=\frac{11}{2}.\frac{4}{11}=2$

 

Answer 4

Bài 7:

a/

$\frac{4}{7}.x=\frac{-1}{5}-\frac{2}{3}=\frac{-13}{15}$

$x=\frac{-13}{15}:\frac{4}{7}=\frac{-91}{60}$

b/

$\frac{2}{9}-\frac{7}{8}x=1$

$\frac{7}{8}x=\frac{2}{9}-1=\frac{-7}{9}$

$x=\frac{-7}{9}:\frac{7}{8}=\frac{-8}{9}$

c.

$\frac{4}{5}+\frac{7}{6}:x=\frac{1}{6}$

$\frac{7}{6}:x=\frac{1}{6}-\frac{4}{5}=\frac{-19}{30}$

$x=\frac{7}{6}:\frac{-19}{30}=\frac{-35}{19}$

d/

$\frac{5}{7}:x-1=\frac{2}{3}$

$\frac{5}{7}:x=1+\frac{2}{3}=\frac{5}{3}$

$x=\frac{5}{7}:\frac{5}{3}=\frac{3}{7}$