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a) \(\left(\frac{1}{3}+\frac{1}{5}\right)+\left(\frac{1}{6}-\frac{1}{5}\right)=\left(\frac{1}{3}+\frac{1}{6}\right)+\left(\frac{1}{5}-\frac{1}{5}\right)=\frac{1}{2}\)
b) \(\frac{3}{16}\times\frac{7}{5}+\frac{3}{5}\times\frac{9}{16}=\frac{21}{80}+\frac{27}{80}=\frac{48}{80}=\frac{3}{5}\)
c) \(\frac{1}{1\times2}+\frac{1}{2\times3}+...+\frac{1}{2020\times2021}=1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+...+\frac{1}{2020}-\frac{1}{2021}\)
\(=1-\frac{1}{2021}=\frac{2020}{2021}\)
d) \(\frac{1}{1\times3}+\frac{1}{3\times5}+...+\frac{1}{2021\times2023}=\frac{1}{2}\times\left(\frac{2}{1\times3}+\frac{2}{3\times5}+...+\frac{2}{2021\times2023}\right)\)
\(=\frac{1}{2}\times\left(1-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+...+\frac{1}{2021}-\frac{1}{2023}\right)\)
\(=\frac{1}{2}\times\left(1-\frac{1}{2023}\right)=\frac{1}{2}\times\frac{2022}{2023}=\frac{1011}{2023}\)
e) \(\frac{3}{2}\times\frac{1}{7}\times\frac{5}{4}+\frac{15}{2}\times\frac{6}{7}\times\frac{1}{4}==\frac{15}{56}+\frac{80}{56}=\frac{95}{56}\)
a)x*4/5:2=6/7 b)6/5:x:5/4=10/15
x*4/5=6/7 x 2 6/5:x=10/15 x 5/4
x*4/5=12/7 6/5:x=5/6
x=12/7:4/5 x=6/5:5/6
x=15/7 x=36/25
a) x * 4/5 : 2 = 6/7
x * 4/5 = 6/7 *2
x *4/5 = 12/7
x = 12/7 : 4/5
x = 15/7
Vậy x = 15/7
1/3 + 1/2 + 1/5 + 12/15 + 22/33 + 16/32
=1/3 + 1/2 + 1/5 + 4/5 + 2/3 + 1/2
=(1/3 + 2/3) + (1/5 + 4/5) + (1/2 + 1/2)
= 1 + 1 + 1
=3
Chúc bạn học tốt !
Phần ở dưới mới là câu hỏi đúng phần câu hỏi ở trên vẫn còn thiếu nha !
Ta có:
\(A=10\times\left(1-\frac{1}{2}+1-\frac{1}{6}+1-\frac{1}{12}+1-\frac{1}{20}+...+1-\frac{1}{90}\right)\)
\(=10\times\left[9-\left(\frac{1}{2}+\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+...+\frac{1}{90}\right)\right]\)
\(=10\times\left[9-\left(\frac{1}{1\times2}+\frac{1}{2\times3}+\frac{1}{3\times4}+\frac{1}{4\times5}+...+\frac{1}{9\times10}\right)\right]\)
\(=10\times\left[9-\left(1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-...-\frac{1}{9}+\frac{1}{9}-\frac{1}{10}\right)\right]\)
\(=10\times\left[9-\left(1-\frac{1}{10}\right)\right]\)
\(=10\times\left(9-\frac{9}{10}\right)\)
\(=10\times\frac{81}{10}\)
\(=81\)
Vậy; A = 81
=.= hk tốt!!
Bài giải
\(\frac{2}{3}+\frac{3}{4}+\frac{4}{5}=\frac{40}{60}+\frac{45}{60}+\frac{48}{60}=\frac{133}{60}\)
\(\frac{8}{5}+\frac{7}{6}+\frac{10}{9}+\frac{1}{2}=\frac{144}{90}+\frac{105}{90}+\frac{100}{90}+\frac{45}{90}=\frac{394}{90}\)
\(\frac{15}{17}-\frac{11}{13}+\frac{3}{26}=\frac{390}{442}+\frac{374}{442}+\frac{51}{442}=\frac{815}{442}\)
\(\frac{9}{12}\text{ x }\frac{4}{3}\text{ : }\frac{8}{5}=\frac{9}{12}\text{ x }\frac{4}{3}\text{ x }\frac{5}{8}=\frac{9\text{ x }4\text{ x }5}{12\text{ x }3\text{ x }8}=\frac{5}{8}\)
\(\frac{4}{5}\text{ x }\frac{15}{8}\text{ : }\frac{5}{7}=\frac{4}{5}\text{ x }\frac{15}{8}\text{ x }\frac{7}{5}=\frac{4\text{ x }15\text{ x }7}{5\text{ x }8\text{ x }5}=\frac{21}{10}\)
\(\frac{2}{3}+\frac{3}{4}+\frac{4}{5}=\frac{40}{60}+\frac{45}{60}+\frac{48}{60}=\frac{133}{60}\)
\(\frac{8}{5}+\frac{7}{6}+\frac{10}{9}+\frac{1}{2}=\frac{144}{90}+\frac{105}{90}+\frac{100}{90}+\frac{45}{90}=\frac{197}{45}\)
\(\frac{15}{17}-\frac{11}{13}+\frac{1}{26}=\frac{390}{442}+\frac{374}{442}+\frac{51}{442}=\frac{815}{442}\)
\(\frac{9}{12}\times\frac{4}{3}:\frac{8}{5}=1:\frac{8}{5}=\frac{5}{8}\)
\(\frac{4}{5}\times\frac{15}{8}:\frac{5}{7}=\frac{3}{2}:\frac{5}{7}=\frac{21}{10}\)
Phương kute kute
Tổng cân nặng cả 3 quả là :
\(\left(\frac{5}{6}+\frac{7}{12}+\frac{3}{4}\right)\text{ : }2=\frac{13}{12}\) kg
Cân nặng của quả táo là:
\(\frac{13}{12}-\frac{5}{6}=\frac{1}{4}\) kg
Cân nặng của quả cam là:
\(\frac{7}{14}-\frac{1}{4}=\frac{1}{3}\)kg
Cân nặng của quả bưởi là:
\(\frac{3}{4}-\frac{1}{4}=\frac{1}{2}\) kg
\(\left(\dfrac{5}{6}+\dfrac{7}{x}\right)-\dfrac{16}{12}=\dfrac{2}{3}\)
\(\Rightarrow\dfrac{5}{6}+\dfrac{7}{x}=\dfrac{2}{3}+\dfrac{16}{12}=\dfrac{8}{12}+\dfrac{16}{12}=\dfrac{24}{12}=2\)
\(\Rightarrow\dfrac{7}{x}=2-\dfrac{5}{6}=\dfrac{12}{6}-\dfrac{5}{6}=\dfrac{7}{6}\)
=> x = 6
(\(\dfrac{5}{6}\) + \(\dfrac{7}{x}\)) - \(\dfrac{16}{12}\) = \(\dfrac{2}{3}\)
\(\dfrac{5}{6}\) + \(\dfrac{7}{x}\) = \(\dfrac{2}{3}\) + \(\dfrac{16}{12}\)
\(\dfrac{5}{6}\) + \(\dfrac{7}{x}\) = 2
\(\dfrac{7}{x}\) = 2 - \(\dfrac{5}{6}\)
\(\dfrac{7}{x}\) = \(\dfrac{1}{6}\)
\(x\) = 6 x (7 : 1)
\(x\) = 6 x 7
\(x\) = 42
#Yu