tìm số tự nhiên x biết:
a) 121/27.54/11<x<100/21:25/126
b) x/17=60/204
c) 6+x/33=7/11
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b;\(\frac{x}{17}=\frac{60}{204}\)
=> \(x=60.17:204=5\)
c; \(6+\frac{x}{33}=\frac{7}{11}\)
=> \(6=\frac{7}{11}-\frac{x}{33}\)
=> \(6=\frac{21}{33}-\frac{x}{33}\)
=> \(6=\frac{21-x}{33}\)
=> \(21-x=198\)
=> \(x=21-198\)
=> \(x=-117\)
a/ Đặt 1/5= a, ta có:
1/5 + 1/10 + 1/20 + 1/40 + ... + 1/1280
= 1/a + 1/2 x a + 1/4 x a + ... + 1/256 x a
A = 1/a + 1/2 x a + 1/4 x a + ... + 1/256 x a
2 x A = 2/a + 1/a + 1/2 x a + 1/4 x a + ... + 1/128 x a
=> A = 2/a - 1/256 x a = 2/5 - 1/1280 = 511/1280
b/
\(\frac{121}{27}.\frac{54}{11}=\frac{11.11.27.2}{27.11}=11.2=22\)
\(\frac{100}{21}:\frac{25}{126}=\frac{100}{21}.\frac{126}{25}=\frac{25.4.21.6}{21.25}=4.6=24\)
=> \(22< n< 24\)
=> \(n=23\)
a) \(A=\frac{1}{5}+\frac{1}{10}+\frac{1}{20}+\frac{1}{40}+...+\frac{1}{1280}\)
\(A.2=\frac{2}{5}+\frac{1}{5}+\frac{1}{10}+\frac{1}{20}+\frac{1}{40}+...+\frac{1}{640}\)
\(A.2-A=\left(\frac{2}{5}+\frac{1}{5}+\frac{1}{10}+\frac{1}{20}+\frac{1}{40}+...+\frac{1}{640}\right)-\left(\frac{1}{5}+\frac{1}{10}+\frac{1}{20}+\frac{1}{40}+...+\frac{1}{1280}\right)\)
\(A=\frac{2}{5}-\frac{1}{1280}=\frac{511}{1280}\)
b) \(\frac{121}{27}.\frac{54}{11}< n< \frac{100}{21}:\frac{25}{126}\)
\(22< n< 24\)
=> n = 23
b) Ta có: \(\frac{121}{27}.\frac{54}{11}< n< \frac{100}{21}:\frac{25}{126}\)
\(\Leftrightarrow22< n< 24\)
\(\Rightarrow n=23\)
\(a,2448:\left[119-\left(x-6\right)\right]=24\)
\(119-\left(x-6\right)=2448:24\)
\(119-\left(x-6\right)=102\)
\(x-6=119-102\)
\(x-6=17\)
\(x=17+6\)
\(\Rightarrow x=23\)
\(b,2016-100\times\left(x+11\right)=128:8\)
\(2016-100\times\left(x+11\right)=16\)
\(100\times\left(x+11\right)=2016-16\)
\(100\times\left(x+11\right)=2000\)
\(x+11=2000:100\)
\(x+11=20\)
\(x=20-11\)
\(\Rightarrow x=9\)
\(a,2448:\left[119-\left(x-6\right)\right]=24\\ 119-\left(x-6\right)=2448:24\\ 119-\left(x-6\right)=102\\ x-6=119-102\\ x-6=17\\ x=17+6\\ x=23\\ b,2016-100\times\left(x+11\right)=128:8\\ 2016-100\times\left(x+11\right)=16\\ 100\times\left(x+11\right)=2016-16\\ 100\times\left(x+11\right)=2000\\ x+11=2000:100\\ x+11=20\\ x=20-11\\ x=9\)
b,\(317-\left(4x+11\right):3=20\\ 317-\left(4x+11\right)=20.3\\ 317-\left(4x+11\right)=60\\ 4x+11=317-60\\ 4x+11=257\\ 4x=257-11\\ 4x=246\\ x=61,5\)
(4X+5) : 3 - 121 : 11 = 4
(4X+5) : 3 - 11 = 4
(4X+5) : 3 = 4 + 11 = 15
(4X+5) = 15 * 3 = 45
4X = 45 - 5 = 40
X = 40 : 4 = 10
Ta có: {4x+5}:3-121:11=4
{4x+5} :3- 11=4
{4x+5}:3=15
4x+5=45
4x=40
x=10
Vậy x=10.
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