Đáp án:
Tìm x
`(``\frac{7}{5}` + `x``)` `-``\frac{2}{5}` = `4`
`\frac{7}{5}` + `x` = `4``+``\frac{2}{5}`
`\frac{7}{5}` + `x` = `\frac{22}{5}`
`x` = `\frac{22}{5}``-``\frac{7}{5}`
`x` = `3`
``(`1\frac{3}{4}` `+` `x``)``-` `\frac{7}{8}` = `5`
`\frac{7}{4}` `+` `x` = `5``+` `\frac{7}{8}`
`\frac{7}{4}` `+` `x` = `\frac{47}{8}`
`x` = `\frac{47}{8}` `-``\frac{7}{4}`
`x` = `\frac{33}{8}`
`(``x``-``\frac{2}{3}``)` `:` `\frac{2}{5}` = `\frac{1}{4}`
`x``-``\frac{2}{3}` = `\frac{1}{4}``×` `\frac{2}{5}`
`x``-``\frac{2}{3}` = `\frac{1}{10}`
`x` = `\frac{1}{10}``+``\frac{2}{3}`
`x` = `\frac{23}{30}`
Tính nhanh
`\frac{1}{30}``+` `\frac{1}{42}``+` `\frac{1}{56}``+``\frac{1}{72}``+``\frac{1}{81}``+``\frac{1}{90}``+``\frac{1}{110}`
= `\frac{1}{5×6}``+` `\frac{1}{6×7}``+` `\frac{1}{7×8}``+``\frac{1}{8×9}``+``\frac{1}{9×9}``+``\frac{1}{9×10}``+``\frac{1}{10×11}`
= `\frac{1}{5}``-` `\frac{1}{6}``+` `\frac{1}{6}``-``\frac{1}{7}``+``\frac{1}{7}``-``\frac{1}{8}``+``\frac{1}{8}``-``\frac{1}{9}``+` `\frac{1}{9}``-``\frac{1}{9}``+` `\frac{1}{9}``-``\frac{1}{10}``+` `\frac{1}{10}``-``\frac{1}{11}`
= `\frac{1}{5}``-``\frac{1}{11}`
= `\frac{6}{55}`
Cho anh câu trả lời hay nhất nha ^.^
#Jen_
