Tính: 12 17 - 5 17 - 4 17
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A =\(\frac{2}{5}\times\frac{4}{7}+\frac{3}{5}\times\frac{4}{7}\) B = \(\frac{17}{13}\times\frac{12}{17}-\frac{4}{13}\times\frac{12}{17}\) C = \(\frac{9}{14}:\frac{6}{7}+\frac{5}{14}:\frac{6}{7}\) D =\(\frac{9}{12}:\frac{7}{9}\times\frac{12}{19}\)
= \(\frac{4}{7}\times\left(\frac{2}{5}+\frac{3}{5}\right)\) =\(\left(\frac{17}{13}-\frac{4}{13}\right)\times\frac{12}{17}\) = \((\frac{9}{14}+\frac{5}{14}):\frac{6}{7}\) = \(\frac{9}{12}\times\frac{9}{7}\times\frac{12}{19}\)
=\(\frac{4}{7}\times1\) = \(1\times\frac{12}{17}\) = \(1:\frac{6}{7}\) = \(\frac{9\times9\times12}{12\times7\times19}\)
=\(\frac{4}{7}\) = \(\frac{12}{17}\) =\(\frac{7}{6}\) = \(\frac{9\times9}{7\times19}=\frac{81}{133}\)
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a)\(\frac{2}{5}+\frac{3}{4}=\frac{8}{20}+\frac{15}{20}=\frac{23}{20}\)
b)\(\frac{7}{12}-\frac{2}{7}+\frac{1}{12}=\frac{7}{12}+\frac{1}{12}-\frac{2}{7}\)\(=\frac{8}{12}-\frac{2}{7}=\frac{56}{84}-\frac{24}{84}=\frac{32}{84}=\frac{8}{21}\)
c) \(\frac{12}{17}-\frac{5}{17}-\frac{3}{17}=\frac{12-5-3}{17}=\frac{4}{17}\)
Chúc bạn học tốt !
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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
\(\frac{2}{5}+\frac{3}{4}=\frac{8}{20}+\frac{15}{20}=\frac{23}{20}\)
\(\frac{7}{12}-\frac{2}{7}+\frac{1}{12}=\left(\frac{7}{12}+\frac{1}{12}\right)-\frac{2}{7}=\frac{2}{3}-\frac{2}{7}=\frac{14}{21}-\frac{6}{21}=\frac{8}{21}\)
\(\frac{12}{17}-\frac{5}{17}-\frac{4}{17}=\frac{12-5-4}{17}=\frac{3}{17}\)
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11 + 2 + 3 = 16 15 + 1 - 6 = 10 17 - 5 - 1 = 11
12 + 3 + 4 = 19 16 + 3 - 9 = 10 17 - 1 - 5 = 11
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a) 5/17 * 8/-7+8/17*-7/3+-7/3*4/17
-40/119 + 12/17 × -7/3
-40/119 + -28/17 =-236/119
b) -10/13 + 5/17 - 3/13 + 12/17 - 11/20
(5/17+12/17)-(10/13+3/13)-11/20
-11/20
a) 5/17 * 8/-7+8/17*-7/3+-7/3*4/17
-40/119 + 12/17 × -7/3
-40/119 + -28/17 =-236/119
b) -10/13 + 5/17 - 3/13 + 12/17 - 11/20
(5/17+12/17)-(10/13+3/13)-11/20
-11/20
![](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)
Phương pháp giải:
Tính nhẩm rồi điền số thích hợp vào chỗ trống.
Lời giải chi tiết:
8 + 9 = 17 | 9 + 8 = 17 | 17 − 8 = 9 | 17 − 9 = 7 |
5 + 7 = 12 | 7 + 5 = 12 | 12 − 5 = 7 | 12 − 7 = 5 |
3 + 8 = 11 | 8 + 3 = 11 | 11 − 3 = 8 | 11 − 8 = 3 |
4 + 9 = 13 | 9 + 4 = 13 | 13 − 4 = 9 | 13 − 9 = 4 |
12 17 - 5 17 - 4 17 = 3 17