40*x=1400
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![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
a) 40 x X = 1400
X = 1400:40
X = 35
b) x : 13 = 205
x = 205 x 13
x = 2665
![](https://rs.olm.vn/images/avt/0.png?1311)
qua de! em hoc lop 5 ; em cung lam duoc cj tran thi thuy ten a!
![](https://rs.olm.vn/images/avt/0.png?1311)
\(S=\frac{10}{56}+\frac{10}{140}+\frac{10}{260}+.......+\frac{10}{1400}\)
\(S=\frac{5}{28}+\frac{5}{70}+\frac{5}{130}+\frac{5}{700}\)
\(\frac{3S}{5}=\frac{3}{4}\times7+\frac{3}{7}\times10+\frac{30}{10}\times13+........+\frac{3}{25}\times28\)
\(\frac{3S}{5}=\frac{1}{4}-\frac{1}{7}+\frac{1}{7}-\frac{1}{10}+\frac{1}{10}-\frac{1}{13}+......+\frac{1}{25}-\frac{1}{28}\)
\(\frac{3S}{5}=\frac{1}{4}-\frac{1}{28}\)
\(\frac{3S}{5}=\frac{3}{14}\)
\(S=\frac{3}{14}\times\frac{5}{3}\)
\(S=\frac{5}{14}\)
Vậy \(S=\frac{5}{14}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(9576:x=1400-1372\)
\(\Rightarrow9576:x=28\)
\(\Rightarrow x=9576:28\)
\(\Rightarrow x=342\)
![](https://rs.olm.vn/images/avt/0.png?1311)
kết quả là
35 đúng thì k
\(40xX=1400\)
\(X=1400:40\)
\(X=35\)
\(K\)
\(NHA~~~!!!\)