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a) - ta có :1/5=8/40 ; 3/8=15/40
8/40<9/40;10/40;11/40;12/40;13/40;14/40<15/40
\(\Rightarrow\) 6 phân số tối giản lớn hơn 1/5 và nhỏ hơn 3/8 là:9/40;1/4;11/40;3/10;13/40;7/20
b) - ta có: 2/5 =12/30 ; 3/5 = 18/30
12/30<13/30;14/30;15/30;16/30;17/30<18/30
\(\Rightarrow\)5p/số khác nhau nằm giữa 2 p/số 1/5 và 3/8 là: 12/30;13/30;14/30;15/30;16/30;17/30
- ta có: 1 - 5/7 =2/7 1 - 5/6 = 1/6
2/7 =12/42 ; 1/6 = 6/42
12/42>11/42;10/42;9/42;8/42;7/42>6/42
\(\Rightarrow\)5p/số khác nhau nằm giữa 2 p/số 5/7 và 5/6 là: 11/42;10/42;9/42;8/42;7/42
c)
\(1\frac{1}{3}\cdot\frac{1}{8}\cdot1\frac{1}{15}\cdot1\frac{1}{24}\cdot1\frac{1}{35}\)
= 4/3 x 9/8 x 16/15 x 25/24 x 36/35
= (4/3 x 9/8) x (16/15 x 25/24) x 36/35
= 3/2 x 10/9 x 26/35
= (3/2 x 10/9) x 36/35
= 5/3 x 36/35
= 12/7
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Ta có ; \(1\dfrac{1}{10}.1\dfrac{1}{11}.....1\dfrac{1}{2011}.1\dfrac{1}{2012}\)
\(=\dfrac{11}{10}.\dfrac{12}{11}.....\dfrac{2012}{2011}.\dfrac{2013}{2012}\)
\(=\dfrac{2013}{10}=201,3\)
1 \(\dfrac{1}{10}\)x 1\(\dfrac{1}{11}\)x 1\(\dfrac{1}{12}\) x...x 1\(\dfrac{1}{2011}\)x 1\(\dfrac{1}{2012}\)
=\(\dfrac{11}{10}\)x \(\dfrac{12}{11}\)x \(\dfrac{13}{12}\)x \(\dfrac{2012}{2011}\)x \(\dfrac{2013}{2012}\)
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\(x:\frac{8}{9}=1\frac{3}{7}\)
\(x:\frac{8}{9}=\frac{10}{7}\)
\(x=\frac{10}{7}.\frac{8}{9}\)
\(x=\frac{80}{63}\)
\(x-1\frac{1}{4}=2\frac{1}{8}\)
\(x-\frac{5}{4}=\frac{17}{8}\)
\(x=\frac{17}{8}+\frac{5}{4}\)
\(x=\frac{17}{8}+\frac{10}{8}\)
\(x=\frac{27}{8}\)
\(x:\frac{8}{9}=1\frac{3}{7}\)
\(x:\frac{8}{9}=\frac{10}{7}\)
\(x=\frac{10}{7}\times\frac{8}{9}\)
\(x=\frac{80}{63}\)
#Y/n
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\(1\)\(\frac{1}{3}x1\)\(\frac{1}{4}x1\)\(\frac{1}{5}x...x1\)\(\frac{1}{8}\)
\(=\frac{4}{3}x\)\(\frac{5}{4}x\)\(\frac{6}{5}\)\(x...x\)\(\frac{9}{8}\)
Tự tính nốt
\(1\frac{1}{3}\times1\frac{1}{4}\times1\frac{1}{5}\times1\frac{1}{6}\times1\frac{1}{7}\times1\frac{1}{8}.\)
= \(\frac{4}{3}\times\frac{5}{4}\times\frac{6}{5}\times\frac{7}{6}\times\frac{8}{7}\times\frac{9}{8}\times\frac{10}{9}\)
= \(\frac{4\times5\times6\times7\times8\times9\times10}{3\times4\times5\times6\times7\times8\times9}\)
= \(\frac{10}{3}\)
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a) (58 + x) : 5 = 18
58 + x = 18 x 5
58 + x = 90
x = 90 - 58
x = 32
d) 320 : x - 10 = 5 x 48 : 24
320 : x - 10 = 10
320 : x = 10 + 10
320 : x = 20
x = 320 : 20
x = 16
c) (1/15 + 1/35 + 1/63) . x = 1
1/9 . x = 1
x = 1 : 1/9
x = 9
\(...=\dfrac{4}{3}x\dfrac{9}{8}x\dfrac{16}{15}x\dfrac{25}{24}=\dfrac{4x9x16x25}{3x8x15x24}=\dfrac{5}{3}\)