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Sửa đề:
24/(3×9) + 24/(9×15) + 24/(15×21) + ... + 24/(57×63)
= 24 × 1/6 × (1/3 - 1/9 + 1/9 - 1/15 + 1/15 - 1/21 + ... + 1/57 - 1/63)
= 4 × (1/3 - 1/63)
= 4 × 20/63
= 80/63
Chỗ \(\dfrac{24}{9\times5}\) là sao em nhỉ? đã đúng đề chưa thế em
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a, \(\dfrac{12}{17}\) x \(\dfrac{21}{63}\) x \(\dfrac{51}{9}\)
= \(\dfrac{3\times4}{17}\) x \(\dfrac{3\times7}{9\times7}\) x \(\dfrac{17\times3}{9}\)
= \(\dfrac{4}{3}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(\dfrac{7}{19}x\dfrac{8}{23}+\dfrac{7}{19}x\dfrac{15}{23}+1\dfrac{7}{19}\)
= \(\dfrac{7}{19}x\left(\dfrac{8}{23}+\dfrac{15}{23}\right)+1+\dfrac{7}{19}\)
=\(\dfrac{7}{19}x1+1+\dfrac{7}{19}\)
= \(\dfrac{7}{19}+1+\dfrac{7}{19}=1\dfrac{14}{19}\) = \(\dfrac{33}{19}\)
\(\dfrac{75}{100}+\dfrac{18}{21}+\dfrac{49}{32}+\dfrac{1}{4}+\dfrac{3}{21}-\dfrac{17}{32}\)
= \(\dfrac{3}{4}+\dfrac{6}{7}+\dfrac{49}{32}+\dfrac{1}{4}+\dfrac{1}{7}-\dfrac{17}{32}\)
= \(\left(\dfrac{3}{4}+\dfrac{1}{4}\right)+\left(\dfrac{6}{7}+\dfrac{1}{7}\right)+\left(\dfrac{49}{32}-\dfrac{17}{32}\right)\)
= 1 + 1 + 1 = 3
\(\dfrac{8}{9}x\dfrac{15}{16}x\dfrac{24}{25}x\dfrac{35}{36}x\dfrac{48}{49}x\dfrac{63}{64}\)
= \(\dfrac{3}{4}\) *Câu này bạn tự sử dụng gạch nhé!
`1,`
`a,`
`7/19 \times 8/23 + 7/19 \times 15/23 + 1 7/19`
`= 7/19 \times 8/23 + 7/19 \times 15/23 + 1 + 7/19`
`= 7/19 \times (8/23 + 15/23 + 1) + 1`
`= 7/19 \times 2 + 1`
`=14/19 + 1`
`= 33/19`
`b,`
`75/100 + 18/21 + 49/32 + 1/4 + 3/21 - 17/32`
`= 75/100 + (18/21 + 3/21) + (49/32 - 17/32) + 1/4`
`= 0,75 + 1 + 1 + 0,25`
`= (0,75 + 0,25) + 1 + 1`
`= 1+1+1=3`
`c,`
`8/9 \times 15/16 \times 24/25 \times 35/36 \times 48/49 \times 63/64`
`=` \(\dfrac{2\times3}{3\times3}\times\dfrac{3\times5}{4\times4}\times\dfrac{3\times4\times2}{5\times5}\times\dfrac{5\times7}{6\times6}\times\dfrac{6\times8}{7\times7}\times\dfrac{7\times9}{8\times8}\)
`= 3/4` (bạn sử dụng gạch, rút gọn các số là được nhé).
![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
a)\(\frac{8}{3}\)
b)\(\frac{1}{5}=0,2\)
c)\(\frac{17}{135}\)
d)\(\frac{2}{3}\)
e)\(\frac{5}{2}=2,5\)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(\dfrac{21}{11}\times\dfrac{22}{17}\times\dfrac{68}{63}:\dfrac{4}{3}=\dfrac{21}{11}\times\dfrac{22}{17}\times\dfrac{68}{63}\times\dfrac{3}{4}=\dfrac{462}{187}\times\dfrac{204}{252}=\dfrac{42}{17}\times\dfrac{17}{21}=\dfrac{2}{1}=2\)
21/11 x 22/17 x 68/63 : 4/3
=( 21/11 x 22/17) x (68/63 : 4/3)
= 42/17 x 17/21
= 2/1 = 2
=3164634 nha bạn.kick vaf kb với mình