tính nhanh 3/4:5/4:3/5:3/8
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`3/4 xx4/5 +3/4xx8/5-3/4xx7/5`
`=3/4xx(4/5+8/5-7/5)`
`=3/4xx5/5`
`=3/4xx1`
`=3/4`
\(A=\dfrac{4}{3}-\left(\dfrac{5}{3}-\dfrac{3}{4}+\dfrac{5}{18}\right)+\left(\dfrac{9}{4}-\dfrac{8}{3}\right)\\ A=\dfrac{4}{3}-\dfrac{5}{3}+\dfrac{3}{4}-\dfrac{5}{18}+\dfrac{9}{4}-\dfrac{8}{3}\\ A=\left(\dfrac{4}{3}-\dfrac{5}{3}-\dfrac{8}{3}\right)+\left(\dfrac{3}{4}+\dfrac{9}{4}\right)-\dfrac{5}{18}\\ A=-3+3-\dfrac{5}{18}\\ A=-\dfrac{5}{18.}\)
1) \(\frac{1}{5}+\frac{3}{17}-\frac{4}{3}+\left(\frac{4}{5}-\frac{3}{17}+\frac{1}{15}\right)\)
\(=\frac{1}{5}+\frac{3}{17}-\frac{4}{3}+\frac{4}{5}-\frac{3}{17}+\frac{1}{15}\)
\(=\left(\frac{1}{5}+\frac{4}{5}\right)+\left(\frac{3}{17}-\frac{3}{17}\right)-\left(\frac{4}{3}-\frac{1}{15}\right)\)
\(=1+0-\frac{19}{15}\)
\(=-\frac{14}{15}\)
Đặt P = ... ( biểu thức đề bài )
Nhận xét: Với \(k\inℕ^∗\) ta có:
\(\frac{k+2}{k!+\left(k+1\right)!+\left(k+2\right)!}=\frac{k+2}{k!+\left(k+1\right).k!+\left(k+2\right).k!}=\frac{k+2}{2.k!\left(k+2\right)}=\frac{1}{2.k!}\)
\(\Rightarrow\)\(P=\frac{1}{2.1!}+\frac{1}{2.2!}+...+\frac{1}{2.6!}=\frac{1}{2}\left(1+\frac{1}{2}+...+\frac{1}{720}\right)=...\)
Bài 7:
Số phần kẹo Hùng đã cho Hà và Hồng là:
\(\dfrac{2}{7}+\dfrac{1}{7}=\dfrac{3}{7}\left(phần\right)\)
Hùng còn lại số phần của gói kẹo là:
\(\dfrac{6}{7}-\dfrac{3}{7}=\dfrac{3}{7}\left(phần\right)\)
1:
2 3/4
5 6/5
3 3/9
7 6/8
2:
1/3 + 2/3 + (3/4 + 1/4) = 2
=2
= 4 5/10
= 51/20
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= 3/14
------------------------------------
= 4/7 - 2/7
= 2/7
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= 17/45
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= 2/3
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= 2 x 1/4
= 1/2
b: \(B=\dfrac{5}{2}-\dfrac{7}{2}+\dfrac{3}{8}+\dfrac{6}{8}+\dfrac{-6}{11}-\dfrac{5}{11}=-2-1+\dfrac{9}{8}=\dfrac{9}{8}-3=-\dfrac{15}{8}\)
c: \(C=\left(\dfrac{4}{3}+\dfrac{7}{3}+\dfrac{1}{3}\right)+\left(\dfrac{2}{5}+\dfrac{3}{5}\right)=4+1=5\)
d: \(D=\dfrac{4}{19}\left(\dfrac{-5}{6}-\dfrac{7}{12}\right)-\dfrac{40}{57}\)
\(=\dfrac{4}{19}\cdot\dfrac{-17}{12}-\dfrac{40}{57}=-1\)
e: \(E=\dfrac{1}{3}\left(\dfrac{4}{5}-\dfrac{9}{5}\right)+\dfrac{2}{3}=\dfrac{2}{3}-\dfrac{1}{3}=\dfrac{1}{3}\)
8/3
= 8/3