Question

Tính, 1/20+2/35+3/70+4/140+5/266+6/475

Answer 1

 

$\frac{1}{20}+\frac{2}{35}+\frac{3}{70}+\frac{4}{140}+\frac{5}{266}+\frac{6}{475}$

$=(\frac{1}{20}+\frac{3}{70}+\frac{4}{140})+(\frac{2}{35}+\frac{5}{266}+\frac{6}{475})$

$=\frac{17}{140}+\frac{31}{350}$

$=\frac{21}{100}$

Answer 2

A = \(\dfrac{1}{20}\) + \(\dfrac{2}{35}\) + \(\dfrac{3}{70}\) + \(\dfrac{4}{140}\) + \(\dfrac{5}{266}\) + \(\dfrac{6}{475}\)

A = \(\dfrac{1}{4\times5}\)+ \(\dfrac{2}{5\times7}\)+ \(\dfrac{3}{7\times10}\)+ \(\dfrac{4}{10\times14}\)+\(\dfrac{5}{14\times19}\)+\(\dfrac{6}{19\times25}\)

A = \(\dfrac{1}{4}\)-\(\dfrac{1}{5}\)+\(\dfrac{1}{5}\)-\(\dfrac{1}{7}\)+\(\dfrac{1}{7}\)-\(\dfrac{1}{10}\)+\(\dfrac{1}{10}\)+\(\dfrac{1}{10}\)-\(\dfrac{1}{14}\)+\(\dfrac{1}{14}\)-\(\dfrac{1}{19}\)+\(\dfrac{1}{19}\)-\(\dfrac{1}{25}\)

A = \(\dfrac{1}{4}\)-\(\dfrac{1}{25}\)

A = \(\dfrac{21}{100}\)