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2/5 + 3/4 = 23/40
7/12 - 2/7 + 1/12 = 25/84 + 1/12 = 8/21
12/17 - 5/17 - 4/17 = 3/17
OK
\(\frac{2}{5}+\frac{3}{4}=\frac{8}{20}+\frac{15}{20}=\frac{23}{20}\)
\(\frac{7}{12}-\frac{2}{7}+\frac{1}{12}=\left(\frac{7}{12}+\frac{1}{12}\right)-\frac{2}{7}=\frac{2}{3}-\frac{2}{7}=\frac{14}{21}-\frac{6}{21}=\frac{8}{21}\)
\(\frac{12}{17}-\frac{5}{17}-\frac{4}{17}=\frac{12-5-4}{17}=\frac{3}{17}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
1 Tính
7/12 - 2/7 + 1/12= (7/12-1/12)+2/7=6/12+2/7=1/2+2/7=7/14+4/14=11/14
12/17-5/17-4/17= 12-5-4/17=3/17
2a, 7/11+3/4+4/11+1/4= (7/11+4/11)+3/4+1/4=11/11+4/4=1+1=2
b)72/99-28/99-14/99= (72-28-14)/99=30/99=10/33
c)69,78+35,97+30,22= (69,78+30,22)+35,97=100+35,97=135,97
d) 83,45-30,98-42,47=83,45-(30,98+42,47)=83,45-73,45=10
![](https://rs.olm.vn/images/avt/0.png?1311)
a) 2/5+3/4=23/20
7/12-2/7+1/12=8//21
12/17-5/17-4/17=3/17
b) 675,39+342,14=1017,53
563,87+403,13-328,35=638,65
a) 2/5+3/4
=8/20+15/20
=21/20
7/12-2/7+1/12
=7/12+1/12-2/7
=1/4-2/7
=7/28-8/28
=-1/28
12/17-5/17-4/17
=12/17-9/17
=3/17
b) 675,39+342,14
= 1017,53
563,87+403,13-328,35
= 967-328,35
= 638,65
![](https://rs.olm.vn/images/avt/0.png?1311)
a) 12/17 : 17/12 + 5/7 : 17/12
= (12/17 + 5/7) : 17/12
= 1 : 17/12
= 12/17
Bài làm
Cách 1 :\(\frac{12}{17}:\frac{17}{12}+\frac{5}{7}:\frac{17}{12}\)
= \(\frac{12}{17}.\frac{12}{17}+\frac{5}{7}.\frac{12}{17}\)
= \(\frac{12}{17}.\left(\frac{12}{17}+\frac{5}{7}\right)\)
= \(\frac{12}{17}.\frac{169}{119}\)
= \(\frac{2028}{2023}\)
Cách 2 : \(\frac{12}{17}:\frac{17}{12}+\frac{5}{7}:\frac{17}{12}\)
= \(\frac{144}{289}+\frac{60}{119}\)
= \(\frac{2028}{2023}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
2/5 +3/4=23/20 7/12 - 2/7 +1/12=32/84 12/17 -5/17 - 4/17=3/17
675,39 + 342,14=1017,54 563,87 + 203,13 - 328,35 =438,65
![](https://rs.olm.vn/images/avt/0.png?1311)
Câu 2:
\(\dfrac{7}{9}\cdot\dfrac{3}{35}=\dfrac{1}{5}\cdot\dfrac{1}{3}=\dfrac{1}{15}\)
\(\dfrac{9}{22}\cdot55=\dfrac{9\cdot55}{22}=\dfrac{9\cdot5}{2}=\dfrac{45}{2}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
2 - 5/6= 7/6
7/8+3/4=`13/8
2/5+3/4=23/20
7/12 - 2/7 + 1/12=8/21
12/17 - 5/17 - 4/17=3/17
![](https://rs.olm.vn/images/avt/0.png?1311)
a) 2/5 + 3/4 =8/20 + 15/20 = 23/20
7/12 - 2/7 + 1/12 = (7/12 + 1/12) - 2/7 = 8/12 - 2/7 = 2/3 - 2/7 = 14/21 - 6/21 =8/21
12/17 - 5/17 - 4/17 = 7/17 - 4/17 = 3/17
b) 675,39 + 342,14 = 1017,53
563,87 + 403,13 - 328,35 = 967 - 328,35 = 638,65
Chúc bạn học tốt
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42/84
3/17 tk mk nhé mk nhanh nhất tk giùm đi
8/21
3/17