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a) $\frac{1}{4} + ..... = \frac{3}{4}$
$\frac{3}{4} - \frac{1}{4} = \frac{1}{2}$
Vậy phân số cần tìm là $\frac{1}{2}$
b) $..... - \frac{3}{5} = \frac{1}{5}$
$\frac{1}{5} + \frac{3}{5} = \frac{4}{5}$
Vậy phân số cần tìm là $\frac{4}{5}$
c) $\frac{2}{3} - ...... = \frac{1}{3}$
$\frac{2}{3} - \frac{1}{3} = \frac{1}{3}$
Vậy phân số cần tìm là $\frac{1}{3}$
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Mình sửa lại đề xíu.
a) \(\frac{75}{100}+\frac{18}{21}+\frac{19}{32}+\frac{1}{4}+\frac{3}{21}+\frac{13}{32}=\frac{3}{4}+\frac{1}{4}+\frac{18}{21}+\frac{3}{21}+\frac{19}{32}+\frac{13}{32}=1+1+1=3\)
b) \(4\frac{2}{5}+5\frac{6}{9}+2\frac{3}{4}+\frac{3}{5}+\frac{1}{3}+\frac{1}{4}=4+\frac{2}{5}+\frac{3}{5}+5+\frac{2}{3}+\frac{1}{3}+2+\frac{3}{4}+\frac{1}{4}\)
\(=4+1+5+1+2+1=14.\)
c) \(\frac{2}{3\cdot5}+\frac{2}{5\cdot7}+\frac{2}{7\cdot9}+...+\frac{2}{41\cdot43}=\frac{5-3}{3\cdot5}+\frac{7-5}{5\cdot7}+\frac{9-7}{7\cdot9}+...+\frac{43-41}{41\cdot43}\)
\(=\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{9}+...+\frac{1}{41}-\frac{1}{43}=\frac{1}{3}-\frac{1}{43}=\frac{43-3}{3\cdot43}=\frac{40}{129}.\)
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a) $\frac{1}{6}:\frac{3}{7} = \frac{1}{6} \times \frac{7}{3} = \frac{7}{{18}}$
b) $\frac{5}{{12}}:\frac{1}{4} = \frac{5}{{12}} \times \frac{4}{1} = \frac{{5 \times 4}}{{12 \times 1}} = \frac{{5 \times 4}}{{4 \times 3 \times 1}} = \frac{5}{3}$
c) $\frac{4}{{15}}:\frac{8}{3} = \frac{4}{{15}} \times \frac{3}{8} = \frac{{4 \times 3}}{{15 \times 8}} = \frac{{4 \times 3}}{{5 \times 3 \times 4 \times 2}} = \frac{1}{{10}}$
d) $\frac{{18}}{5}:\frac{9}{{10}} = \frac{{18}}{5} \times \frac{{10}}{9} = \frac{{18 \times 10}}{{5 \times 9}} = \frac{{9 \times 2 \times 5 \times 2}}{{5 \times 9}} = 4$
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a) \(3\frac{4}{7}\times2\frac{4}{5}\)
\(=\frac{25}{7}\times\frac{14}{5}=\frac{350}{35}=10\)
b) \(\frac{4}{5}:\frac{1}{2}+\frac{17}{3}\)
\(=\frac{8}{5}+\frac{17}{3}\)
\(=\frac{109}{15}\)
c) \(5\frac{1}{3}-2\frac{1}{6}\)
\(=\frac{16}{3}-\frac{13}{6}\)
\(=\frac{32}{6}-\frac{13}{6}=\frac{19}{6}\)
d) \(4\frac{1}{2}:2\frac{1}{4}\)
\(=\frac{9}{2}:\frac{9}{4}=\frac{45}{18}\)
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\(x-\frac{4}{5}=\frac{4}{5}+\left(\frac{3}{7}+\frac{3}{5}\right)\)
\(x-\frac{4}{5}=\frac{4}{5}+\frac{36}{35}\)
\(x-\frac{4}{5}=\frac{64}{35}\)
\(x=\frac{64}{35}+\frac{4}{5}\)
\(x=\frac{92}{35}\)
\(x-\frac{4}{5}=\frac{4}{5}+\left(\frac{3}{7}+\frac{3}{5}\right)\)
\(x=\frac{4}{5}+\frac{3}{7}+\frac{3}{5}+\frac{4}{5}\)
\(x=\frac{11}{5}+\frac{3}{7}\)
\(x=\frac{11\times7+3\times5}{7\times5}\)
\(x=\frac{92}{35}\)
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a) Quy đồng mẫu số 3 phân số $\frac{1}{2}$ ; $\frac{3}{4}$ ; $\frac{5}{8}$, chọn mẫu số chung là 8
$\frac{1}{2} = \frac{{1 \times 4}}{{2 \times 4}} = \frac{4}{8}$ $\frac{3}{4} = \frac{{3 \times 2}}{{4 \times 2}} = \frac{6}{8}$
Ta có $\frac{6}{8} > \frac{5}{8} > \frac{4}{8}$ nên $\frac{3}{4} > \frac{5}{8} > \frac{1}{2}$
Vậy các phân số theo thứ tự từ lớn đến bé là $\frac{3}{4}$ ; $\frac{5}{8}$ ; $\frac{1}{2}$
b) Quy đồng mẫu số 4 phân số $\frac{2}{3}$ ; $\frac{3}{4}$ ; $\frac{5}{6}$ ; $\frac{7}{{12}}$, chọn mẫu số chung là 12
$\frac{2}{3} = \frac{{2 \times 4}}{{3 \times 4}} = \frac{8}{{12}}$ $\frac{3}{4} = \frac{{3 \times 3}}{{4 \times 3}} = \frac{9}{{12}}$
$\frac{5}{6} = \frac{{5 \times 2}}{{6 \times 2}} = \frac{{10}}{{12}}$
Ta có $\frac{{10}}{{12}} > \frac{9}{{12}} > \frac{8}{{12}} > \frac{7}{{12}}$ nên $\frac{5}{6} > \frac{3}{4} > \frac{2}{3} > \frac{7}{{12}}$
Vậy các phân số theo thứ tự từ lớn đến bé là $\frac{5}{6};\,\,\frac{3}{4};\,\,\frac{2}{3};\,\,\frac{7}{{12}}$
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a) $\frac{1}{2} - \frac{1}{4} = \frac{2}{4} - \frac{1}{4} = \frac{1}{4}$
b) $\frac{2}{3} - \frac{4}{{15}} = \frac{{10}}{{15}} - \frac{4}{{15}} = \frac{6}{{15}} = \frac{2}{5}$
c) $\frac{3}{5} - \frac{{10}}{{25}} = \frac{{15}}{{25}} - \frac{{10}}{{25}} = \frac{5}{{25}} = \frac{1}{5}$
\(\frac{5}{4}-\frac{4}{3}\)
= \(\frac{15}{12}-\frac{16}{12}\)
= \(-\frac{1}{12}\)
HT
\(\frac{5}{4}\)-\(\frac{4}{3}\)
= \(\frac{5x3}{4x3}\)- \(\frac{4x4}{3x4}\)
= \(\frac{15}{12}\)- \(\frac{16}{12}\)
= -\(\frac{1}{12}\)