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\(\frac{1}{1\times2}+\frac{1}{2\times3}+\frac{1}{3\times4}+...+\frac{1}{999\times1000}+1\)
\(=\frac{1}{2}+\frac{1}{6}+\frac{1}{12}+....+\frac{1}{999000}+1\)
\(=1-\frac{1}{1000}+1\)
\(=\frac{1999}{1000}\)
X đầu tiên : 32 phần 32
X thứ hai : 36 phần 120
X thứ ba : 18 phần 21
X - ( 1/4 + 1/8 ) = 5/8
X - 3/8 = 5/8
X = 5/8 + 3/8
X = 1
\(a.32,5-3\cdot0,87=32,5-2,61=29,89\)
\(8,5\cdot\left(1\dfrac{1}{2}+\dfrac{4}{4}\right):5=8,5\cdot\left(\dfrac{3}{2}+\dfrac{4}{4}\right):5\\ =8,5\cdot\left(\dfrac{6}{4}+\dfrac{4}{4}\right):5\\ =8,5\cdot\dfrac{10}{4}:5\\ =\dfrac{85}{4}:5\\ =\dfrac{17}{4}\)
\(b.30,96-6,45+14,4:3=30,96-6,45+4,8\\ =29,31\)
\(\dfrac{2}{5}\cdot\left(\dfrac{4}{5}-\dfrac{1}{2}\right)=\dfrac{2}{5}\cdot\left(\dfrac{8}{10}-\dfrac{5}{10}\right)\\ =\dfrac{2}{5}\cdot\dfrac{3}{10}=\dfrac{3}{25}\)
bài 2
\(a.2,5\cdot12,5\cdot8\cdot0,4=\left(2,5\cdot0,4\right)\left(12,5\cdot8\right)\\ =1\cdot100=100\)
b,\(\dfrac{12}{15}\cdot\dfrac{5}{6}\cdot\dfrac{3}{20}\cdot\dfrac{32}{5}=\dfrac{12\cdot5\cdot3\cdot32}{15\cdot6\cdot20\cdot5}\\ =\dfrac{3\cdot4\cdot5\cdot3\cdot4\cdot8}{3\cdot5\cdot2\cdot3\cdot5\cdot4\cdot5}=\dfrac{16}{25}\)
Bài 1:
a) \(32.5-3\cdot0.87=32.5-2.61=29.89\)
\(8.5\cdot\left(1\dfrac{1}{2}+\dfrac{4}{4}\right):5=8.5\cdot\dfrac{5}{2}:5=\dfrac{17}{2}\cdot\dfrac{5}{2}:5=\dfrac{85}{4}\cdot\dfrac{1}{5}=\dfrac{17}{4}\)
Phuong lê thảo thanh đây nhé!
\(x+\frac{1}{2}\cdot\frac{1}{5}=\frac{3}{4}\)
\(\Leftrightarrow x+\frac{1}{10}=\frac{3}{4}\)
\(\Leftrightarrow x=\frac{3}{4}-\frac{1}{10}\)
\(\Leftrightarrow x=\frac{15}{20}-\frac{2}{20}=\frac{13}{20}\)
Vậy x=\(\frac{13}{20}\)
2 - x = 1/5 : 1/4
2 - x = 1/5 * 4
2 - x = 4/5
x = 2 - 4/5
x = 6/5
3 - x = 1/3 : 1/6
3 - x = 1/3 * 6
3 - x = 2
x = 3 - 2
x = 1
b) 1/3 * 1/2 + 1/5 * 1/2
= 1/2 * (1/3 + 1/5)
= 1/2 * 8/15
= 4/15
373737/414141 : 4545/4141
= 37/41 : 45/41
= 37/41 * 41/45
= 37/45
2727/4242 + 13/42 + 444444/424242
= 9/14 + 13/42 + 22/21
= 2
\(\left(1-\dfrac{1}{2}\right)\times\left(1-\dfrac{1}{2}\right)\times\left(1-\dfrac{1}{3}\right)\times\left(1-\dfrac{1}{4}\right)\times\left(1-\dfrac{1}{5}\right)\)
\(=\dfrac{1}{2}\times\dfrac{1}{2}\times\dfrac{2}{3}\times\dfrac{3}{4}\times\dfrac{4}{5}\)
\(=\dfrac{1}{2}\times\dfrac{1}{5}\)
\(=\dfrac{1}{10}\)