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Theo đề bài: (X+3)+(X+7)+(X+11)+...........+(X+79)=860
X.20+(3+7+11+.........+79)=86
SSH: (79-3):4+1:2=10 (cặp)
SC:79+3=82
3+7+11+.....+79=10.82=820
X.20+820=860
X.20 =860-820=40
X =40:20
X =2
Đ/S;X=2
\(\left(x+3\right)+\left(x+7\right)+\left(x+11\right)+...+\left(x+79\right)=860\)
\(\Leftrightarrow20x+\left(3+7+11+...+79\right)=860\)
\(\Leftrightarrow20x+20.\frac{79+3}{2}=860\)
\(\Leftrightarrow20x+820=860\)
\(\Rightarrow x=2\)
Vậy \(x=2\)
![](https://rs.olm.vn/images/avt/0.png?1311)
(x+x+....+x)+(3+7+11+.....+79)=860
20x+820=860
20x=860-820
20x=40
x=40:20
x=2
Fan tf thì kb nha
![](https://rs.olm.vn/images/avt/0.png?1311)
(x + 3) + (x + 7) + (x + 11) + ... + (x + 79) = 860
=> x + 3 + x + 7 + x + 11 + ... + x + 79 = 860
=> (x + x + x + ... + x) + (3 + 7 + 11 + ... + 79) = 860
=> 20x + (79 + 3).20 : 2 = 860
=> 20x + 82.20 : 2 = 860
=> 20x + 82.10 = 860
=> 20x + 820 = 860
=> 20x = 40
=> x = 2
vậy_
#)Giải :
\(\left(x+3\right)+\left(x+7\right)+...+\left(x+79\right)=860\)
\(\left(x+x+...+x\right)+\left(3+7+...+79\right)=860\)(trong mỗi ngoặc có 20 số hạng)
\(x\times20+\frac{\left(79+3\right)\times20}{2}=860\)
\(x\times20+820=860\)
\(x\times20=860-820\)
\(x\times20=40\)
\(x=40\div20\)
\(x=2\)
![](https://rs.olm.vn/images/avt/0.png?1311)
9/11 : y = 2/5 + 2/7
9/11 :y = 24/35
y = 9/11 : 24/35
y = 105/88
y * 3/11 = 3/4 - 6/11
y * 3/11 = 9/44
y = 9/44 : 3/11
y = 3/4
Bạn thamkhaor nhé
![](https://rs.olm.vn/images/avt/0.png?1311)
X là :
( 79 + 7 ) : 2 = 43
Y là :
79 - 43 = 36
Đáp số : 43 và 36
Số y là :
( 79 - 7 ) : 2 = 36
Số x là :
79 - 36 = 43
HT
![](https://rs.olm.vn/images/avt/0.png?1311)
a) y : 4/11 x 3/5 = 27/4
y : 4/11 = 27/4 : 3/5
y : 4/11 = 45/4
y = 45/4 x 4/11
y = 45/11
b) y + 7/2 - 5/9 = 14/3
y + 7/2 = 14/3 + 5/9
y + 7/2 = 47/9
y = 47/9 - 7/2
y = 31/18
a) y : 4/11 x 3/5 = 27/4
y : 4/11 = 27/4 : 3/5
y : 4/11 = 45/4
y = 45/4 x 4/11
y = 45/11
b) y + 7/2 - 5/9 = 14/3
y + 7/2 = 14/3 + 5/9
y + 7/2 = 47/9
y = 47/9 - 7/2
y = 31/18
![](https://rs.olm.vn/images/avt/0.png?1311)
bài 1 :
\(\frac{5}{12}\) + \(\frac{1}{3}\) = \(\frac{5}{12}\) + \(\frac{4}{12}\) = \(\frac{5+4}{12}\) = \(\frac{9}{12}\) = \(\frac{3}{4}\)
1 - \(\frac{3}{4}\) = \(\frac{4}{4}\) - \(\frac{3}{4}\) = \(\frac{4-3}{4}\) = \(\frac{1}{4}\)
2 x \(\frac{3}{11}\) = \(\frac{2x3}{11}\) = \(\frac{6}{11}\)
\(\frac{8}{7}\): 4 = \(\frac{8}{7x4}\) = \(\frac{8}{28}\) = \(\frac{2}{7}\)
bài 2 :
\(\frac{2}{5}\) : y = \(\frac{1}{3}\)
y = \(\frac{2}{5}\) : \(\frac{1}{3}\)
y = \(\frac{6}{5}\)
y : \(\frac{7}{11}\) = 22
y = 22 x \(\frac{7}{11}\)
y = 14
ai thấy đúng tk nha
![](https://rs.olm.vn/images/avt/0.png?1311)
a, \(y=\dfrac{7}{11}-\dfrac{5}{14}=\dfrac{98-55}{154}=\dfrac{43}{154}\)
b, \(y=\dfrac{8}{9}.\dfrac{4}{7}=\dfrac{32}{63}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
Bài 1 :
\(\frac{2}{19}+\frac{4}{5}+1\frac{7}{9}+\frac{1}{5}\)
\(=\frac{2}{19}+1\frac{7}{9}+\left(\frac{4}{5}+\frac{1}{5}\right)\)
\(=\frac{2}{19}+1\frac{7}{9}+1\)
\(=\frac{493}{171}\)
\(\frac{1}{11}+\frac{2}{11}+\frac{3}{11}+\frac{4}{11}+\frac{5}{11}+\frac{6}{11}+\frac{7}{11}+\frac{8}{11}+\frac{9}{11}+\frac{10}{11}\)
\(=\left(\frac{1}{11}+\frac{10}{11}\right)+\left(\frac{2}{11}+\frac{9}{11}\right)+\left(\frac{3}{11}+\frac{8}{11}\right)+\left(\frac{4}{11}+\frac{7}{11}\right)+\left(\frac{5}{11}+\frac{6}{11}\right)\)
\(=1+1+1+1+1\)
\(=5\)
Bài 2 :
y : (23 + 27) = 9 1000 : (y x 25) = 8
y : 50 = 9 y x 25 = 1000 : 8
y = 9 x 50 y x 25 = 125
y = 450 y = 125 : 25
133 : (190 : y) = 7 y = 5
190 : y = 133 : 7 450 : (y + 42) = 9
190 : y = 19 y + 42 = 450 : 9
y = 190 : 19 y + 42 = 50
y = 10 y = 50 - 42
y = 8
[y + 3] + [y + 7] + [y + 11] + ... + [y + 79] = 860
20y + (3 + 7 + 11 + ..... + 79) = 860
Áp dụng công thức tính tổng dãy số ta có :
3 + 7 + 11 + ..... + 79 = 20 . 41 = 820
=> 20y + 820 = 860
=> 20y = 40
=> y = 2