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1-19/21=2/21
1-15/17=2/17
1-23/25=2/25
1-27/29=2/29
Vì 2/17>2/21>2/25>2/29 nên theo thứ tự bé đến lớn là 15/17;19/21;23/25;27/29
19/21 = 21/21 - 2/21 = 1 - 2/21
15/17 = 17/17 - 2/17 = 1- 2/17
23/25 = 25/25 - 2/25 = 1 - 2/25
27/29 = 29/29 - 2/29 = 1 - 2/29
Ta có: 2/17>2/21>2/25>2/29
Do đó: 15/17<19/21<23/25<27/29
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\(\dfrac{75}{100}=\dfrac{3}{4};\dfrac{63}{126}=\dfrac{1}{2}\\ \dfrac{36}{27}=1\dfrac{1}{3};\dfrac{81}{54}=1\dfrac{1}{2};\dfrac{105}{405}=\dfrac{7}{27}\)
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`27/81=(27:27)/(81:27)=1/3`
`57/76=(57:19)/(76:19)=3/4`
`35/84=(35:7)/(84:7)=5/12`
`MSC:12`
`1/3=(1xx4)/(3xx4)=4/12`
`3/4=(3xx3)/(4xx3)=9/12`
`5/12` giữ nguyên
\(\dfrac{27}{81}=\dfrac{1}{3}\); \(\dfrac{57}{76}=\dfrac{3}{4}\); \(\dfrac{35}{84}=\dfrac{5}{12}\)
\(\dfrac{1}{3}=\dfrac{4}{12}\)
\(\dfrac{3}{4}=\dfrac{9}{12}\)
Giữa nguyên 5/12
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\(\frac{10}{25};\frac{14}{18};\frac{15}{20};\frac{16}{40};\frac{30}{48};\frac{63}{81}\)
\(=>\frac{10}{25}=\frac{2}{5}\)\(;\frac{14}{18}=\frac{7}{9};\frac{15}{20}=\frac{3}{4};\frac{16}{40}=\frac{2}{5};\frac{30}{48}=\frac{5}{8};\frac{63}{81}=\frac{7}{9}\)
\(=>\frac{2}{5};\frac{7}{9};\frac{3}{4};\frac{2}{5};\frac{5}{8};\frac{7}{9}\)
Phân số bằng nhau là : \(\frac{10}{25};\frac{16}{40}\)và \(\frac{14}{18};\frac{63}{81}\)
\(\frac{10}{15}=\frac{2}{3}\) \(\frac{14}{18}=\frac{7}{9}\) \(\frac{15}{20}=\frac{3}{4}\)
\(\frac{16}{40}=\frac{2}{5}\) \(\frac{36}{48}=\frac{3}{4}\) \(\frac{63}{81}=\frac{7}{9}\)
Vậy các phân số bằng nhau là :
\(\frac{15}{20}=\frac{36}{48}\) ; \(\frac{14}{18}=\frac{63}{81}\)
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\(a.\dfrac{5}{10}=\dfrac{1}{2}=\dfrac{1\times3}{2\times3}=\dfrac{3}{6}\)
\(\dfrac{25}{75}=\dfrac{1}{3}=\dfrac{1\times2}{3\times2}=\dfrac{2}{6}\)
\(b.\dfrac{42}{56}=\dfrac{3}{4}=\dfrac{3\times2}{4\times2}=\dfrac{6}{8}\)
\(\dfrac{18}{48}=\dfrac{3}{8}\)
\(c.\dfrac{27}{81}=\dfrac{1}{3}=\dfrac{1\times4}{3\times4}=\dfrac{4}{12}\)
\(\dfrac{57}{76}=\dfrac{3}{4}=\dfrac{3\times3}{4\times3}=\dfrac{9}{12}\)
\(\dfrac{35}{84}=\dfrac{5}{12}\)
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- Các phân số < 1 là : `3/7;12/19` ( Do tử < mẫu )
- Các phân số = 1 là : `10/10;25/25` ( Do tử = mẫu )
- Các phân số > 1 là : `8/5;27/16` ( Do tử > mẫu )
Phân số bé hơn 1: 3/7 ; 12/19
Phân số bằng 1 là: 25/25; 10/10
Còn lại là lớn hơn 1
25/27 + 19/81
= 75/81 + 19/81
= 94/81
25/27+19/81
=75/81+19/81
=94/81