A=1/2-1/3+1/3-1/4+...+1/149-1/150

=1/2-1/150

=37/75

B=3A=37/25

\(A=\frac{1}{2\cdot3}+\frac{1}{3\cdot4}+\frac{1}{4\cdot5}+...+\frac{1}{149\cdot150}\)

\(A=\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+...+\frac{1}{149}-\frac{1}{150}\)

\(A=\frac{1}{2}-\frac{1}{150}\)

\(A=\frac{75}{150}-\frac{1}{150}\)

\(A=\frac{74}{150}=\frac{37}{75}\)

Vậy \(A=\frac{37}{75}\)

a: \(12\dfrac{1}{3}-\left(3\dfrac{3}{4}+4\dfrac{3}{4}\right)\)

\(=\dfrac{37}{3}-3-4-\dfrac{3}{2}\)

\(=\dfrac{74-9}{6}-7=\dfrac{65}{6}-7=\dfrac{65-42}{7}=\dfrac{23}{7}\)

b: \(3\dfrac{5}{6}+2\dfrac{1}{6}\cdot6\)

\(=3+\dfrac{5}{6}+\dfrac{13}{6}\cdot6\)

\(=16+\dfrac{5}{6}=\dfrac{101}{6}\)

c: \(3\dfrac{1}{2}+4\dfrac{5}{7}-5\dfrac{5}{14}\)

\(=3+\dfrac{1}{2}+4+\dfrac{5}{7}-5-\dfrac{5}{14}\)

\(=2+\dfrac{7+10-5}{14}=2+\dfrac{12}{14}=2+\dfrac{6}{7}=\dfrac{20}{7}\)

d: \(=\dfrac{9}{2}+\dfrac{1}{2}:\dfrac{11}{2}=\dfrac{9}{2}+\dfrac{1}{11}=\dfrac{99+2}{22}=\dfrac{101}{22}\)

các bn giải mk nha

Ta có 1/2*3=1/2-1/3;

         1/3*4=1/3-1/4

       ......................(tương tự với các số khác)

         1/149*150=1/149-1/150

=>A=1/2-1/3+1/3-1/4+1/4-1/5+...-1/149+1/149-1/150=1/2-1/150

A=75/150-1/150=74/150=37/75

Vậy A= 37/75

a) 3 2/7 - 2/5 + 5/7 - 3/5

= 3 + 2/7 - (2/5 + 3/5) + 5/7

= 3 + (2/7 + 5/7) - 1

= 3 + 1 - 1

= 3

b) 5 4/7 - 4/9 + 1 3/7 - 5/9

= 5 + 4/7 - 4/9 + 1 + 3/7 - 5/9

= (5 + 1) + (4/7 + 3/7) - (4/9 + 5/9)

= 6 + 1 - 1

= 6

a) \(3\dfrac{2}{7}-\dfrac{2}{5}+\dfrac{5}{7}-\dfrac{3}{5}\)

\(=\left(\dfrac{23}{7}+\dfrac{5}{7}\right)-\left(\dfrac{2}{5}+\dfrac{3}{5}\right)\)

\(=4-1\)

\(=3\)

b) \(5\dfrac{4}{7}-\dfrac{4}{9}+1\dfrac{3}{7}-\dfrac{5}{9}\)

\(=\left(\dfrac{32}{7}+\dfrac{10}{7}\right)-\left(\dfrac{4}{9}+\dfrac{5}{9}\right)\)

\(=6-1\)

\(=5\)

a) \(3\dfrac{2}{7}-\dfrac{2}{5}+\dfrac{5}{7}-\dfrac{3}{5}\)

\(=\left(\dfrac{23}{7}+\dfrac{5}{7}\right)-\left(\dfrac{2}{5}+\dfrac{3}{5}\right)\)

\(=4-1\)

\(=3\)

b) \(5\dfrac{4}{7}-\dfrac{4}{9}+1\dfrac{3}{7}-\dfrac{5}{9}\)

\(=\left(\dfrac{39}{7}+\dfrac{10}{7}\right)-\left(\dfrac{4}{9}+\dfrac{5}{9}\right)\)

\(=7-1\)

\(=6\)

a) Số thứ nhất là :

\(\left(\frac{9}{5}+\frac{1}{4}\right)\div2=\frac{41}{40}\)

Số thứ hai là :

\(\frac{9}{5}-\frac{41}{40}=\frac{31}{4}\)

b) Số thứ nhất là :

\(\left(\frac{7}{3}+\frac{1}{6}\right)\div2=\frac{23}{9}\)

Số thứ hai là :

\(\frac{23}{9}-\frac{1}{6}=\frac{119}{54}\)

c) Số thứ nhất là :

\(\left(\frac{5}{2}+\frac{3}{8}\right)\div2=\frac{23}{8}\)

Số thứ hai là :

\(\frac{23}{8}-\frac{3}{8}=\frac{20}{8}\)

CỘNG

a) \(\frac{9}{5}\)+\(\frac{1}{4}\)=\(\frac{9x4}{5x4}\)+\(\frac{1x5}{4x5}\)=\(\frac{36}{20}\)+\(\frac{5}{20}\)=\(\frac{41}{20}\)

b) \(\frac{7}{3}\)+\(\frac{1}{6}\)= \(\frac{7x6}{3x6}\)+\(\frac{1x3}{6x3}\)=\(\frac{42}{18}\)+\(\frac{3}{18}\)=\(\frac{45}{18}\)

c) \(\frac{5}{2}\)+\(\frac{3}{8}\)=\(\frac{5x8}{2x8}\)+\(\frac{3x2}{8x2}\)=\(\frac{40}{16}\)+\(\frac{6}{16}\)=\(\frac{46}{16}\)

TRỪ

a) \(\frac{9}{5}\)-\(\frac{1}{4}\)=\(\frac{9x4}{5x4}\)\(\frac{1x5}{4x5}\)=\(\frac{36}{20}\)--\(\frac{5}{20}\)=\(\frac{31}{20}\)

b) \(\frac{7}{3}\)-\(\frac{1}{6}\)=\(\frac{7x6}{3x6}\)- \(\frac{1x3}{6x3}\)=\(\frac{42}{18}\)-\(\frac{3}{18}\)=\(\frac{39}{18}\)

c)\(\frac{5}{2}\)-\(\frac{3}{8}\)=\(\frac{5x8}{2x8}\)-\(\frac{3x2}{8x2}\)=\(\frac{40}{16}\)-\(\frac{6}{16}\)=\(\frac{34}{16}\)