![](https://rs.olm.vn/images/avt/0.png?1311)
Hãy nhập câu hỏi của bạn vào đây, nếu là tài khoản VIP, bạn sẽ được ưu tiên trả lời.
![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(B=\dfrac{4}{1\times3}+\dfrac{4}{3\times5}+\dfrac{4}{5\times7}+...+\dfrac{4}{47\times49}+\dfrac{4}{49\times51}\)
\(=2\times\left(\dfrac{2}{1\times3}+\dfrac{2}{3\times5}+\dfrac{2}{5\times7}+...+\dfrac{2}{47\times49}+\dfrac{2}{49\times51}\right)\)
\(=2\times\left(1-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{7}+...+\dfrac{1}{47}-\dfrac{1}{49}+\dfrac{1}{49}-\dfrac{1}{51}\right)\)
\(=2\times\left(1-\dfrac{1}{51}\right)\)
\(=2\times\dfrac{50}{51}\)
\(=\dfrac{100}{51}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
a.5/6 - 26/5 X 1/13 = 13/30
b.( 19/23 - 22/46 ) X 23/46 = 3/23
c.25/8 x 14/30 = 35/24
d.( 3/4 x 5/7 ) x ( 20/9 x 14/15 ) = 10/9
e.4/35 x 25/32 x 38/24 = 95/672
g. 1/2 x 3/4 x 2/3 x 4/5 = 1/5
h.5/6 x 11/4 - 5/4 x 23/6 = -5/2
i.9/16 x 13/4 - 9/4 x 5/16 + 9/16 x 17/4 = 225/64
k.( 7 x 1/3 ) x ( 1/7 x 6 ) = 2
m.2/3 x ( 3/5 + 3/7 ) = 34/35
n.4/5 x ( 5/8 + 7/4 ) = 19/10
p.( 1/33 + 31/333 - 341/3333 ) x ( 1/2 - 1/3 - 1/6 ) = 0
mih giành cả nửa tiếng để giải đó , k nha
![](https://rs.olm.vn/images/avt/0.png?1311)
\(\dfrac{49}{28}:\dfrac{5}{4}.\dfrac{6}{7}=\dfrac{49}{28}.\dfrac{4}{5}.\dfrac{6}{7}=\dfrac{49.4.6}{28.5.7}=\dfrac{7.7.4.6}{4.7.5.7}=\dfrac{6}{5}\)
\(\dfrac{49}{28}:\dfrac{5}{4}\times\dfrac{6}{7}\)
= \(\dfrac{49}{28}\times\dfrac{4}{5}\times\dfrac{6}{7}\)
= \(\dfrac{7\times7}{4\times7}\) x \(\dfrac{4}{5}\) x \(\dfrac{6}{7}\)
= \(\dfrac{6}{5}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
a)\(\frac{21}{11}x\frac{22}{17}x\frac{68}{63}\)
=\(\frac{21x22x68}{11x17x63}\)
=\(\frac{21x11x2x17x4}{11x17x21x3}\)
=\(\frac{2x4}{3}\)
=\(\frac{8}{3}\)
b)\(\frac{5}{14}x\frac{7}{13}x\frac{26}{25}\)
=\(\frac{5x7x26}{14x13x25}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
5 x 7 x 77 - 7 x 60 + 49 x 25 -15 x 42
= 5x7x77 - 7x5x12 + 7x7x5x5 - 5x3x7x6
= 35 x77 - 35x12 + 35x35 - 35x18
= 35 x ( 77-12+35-18 )
= 35 x 82 = 2870
![](https://rs.olm.vn/images/avt/0.png?1311)
\(\frac{1}{5}\cdot\frac{1}{7}+\frac{4}{5}+\frac{1}{5}\cdot\frac{12}{7}-1-\frac{1}{5}\cdot\frac{6}{7}\)
\(=\frac{1}{5}\cdot\left(\frac{1}{7}+\frac{12}{7}-\frac{6}{7}\right)-\left(1-\frac{4}{5}\right)\)
\(=\frac{1}{5}.1-\frac{1}{5}\)
\(=\frac{1}{5}-\frac{1}{5}=0\)
=35 . 77 - 35.12 + 35 . 35 - 35.18
=35.(77-12+35-18)
=35.82
=2870