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Ta có:(x + 1)+(x+3)+...+(x+9)=75
=>5x + (1+3+...+9)=75
=>5x + 25=75
=>5x =50
=>x = 10
a. (x+1)+(x+3)+(x+5)+(x+7)+(x+9)=75
=>(x+x+x+x+x)+(1+3+5+7+9)=75
=>Xx5+25=75
=>Xx5=75-25
=>Xx5=50
=>x=50:5
=>x=10
b. sai đề
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20x +(1+6+11+.....+96)=990
20x + 970=990
20x=990-997
20x=20
x=1
(x+1)+(x+6)+...+(x+96)=990
\(\Leftrightarrow\)20x+(1+6+11+...+96) = 990
\(\Leftrightarrow\)20x + \(\frac{\left(1+96\right)\times\left[\left(96-1\right):5+1\right]}{2}\)= 990
\(\Leftrightarrow\)20x+970=990
\(\Leftrightarrow\)20x=990-970=20
\(\Leftrightarrow\)x=1
Vậy x= 1
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a)\(\frac{27}{5}\text{x}\frac{91}{12}\text{x}\frac{125}{9}\text{x}\frac{96}{13}=\frac{27}{9}\text{x}\frac{91}{13}\text{x}\frac{125}{5}\text{x}\frac{96}{12}=3\text{x}7\text{x}25\text{x}8\)
Đến đây tự tính nha !
b)\(\frac{2539}{35}\text{x}\frac{7}{90}+\frac{561}{35}\text{x}\frac{7}{90}=\frac{7}{90}\text{x}\left(\frac{2539}{35}+\frac{561}{35}\right)=\frac{7}{90}\text{x}\frac{3100}{35}=\frac{3100}{90}\text{x}\frac{7}{35}=\frac{310}{9}\text{x}\frac{1}{5}=\frac{62}{9}\)
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x+2/2+x+ 2/6 +x+ 2/12 +...+x+ 2/110 = 130/11
=> x +2/1.2 + x +2/2.3 + x +2/3.4 +...+ x +2/10.11 = 130/11
=> 10 x + 2/1.2+2/2.3+....+2/10.11 = 130/11
=> 10 x + 2. [ 1/1.2+1/2.3+...+1/10.11] = 130/11
=> 10 x + 2. [1-1/2+1/2-1/3+...+1/10-1/11] = 130/11
=> 10 x + 2 [1-1/11] = 130/11
=> 10 x + 2 x 10/11 = 130/11
=> 10 x +20/11 = 130/11
=> 10 x = 10 => x= 10 : 10=1
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Số số hạng :
( 36 - 1) : 5 + 1 = 8 ( số hạng)
Tổng của dãy :
( 36 + 1) x 8 : 2 = 148
8x + 148 = 228
8x = 228 -148
8x =80
x = 80 : 8
x = 10
8x+(1+6+11+16+21+26+31+36)=228
8x+148=228
8x=228-148
8x=80
x=80/8
x=10