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1 + 1 + 2 + 2 + 3 + 3 + 4 + 4 + 5 + 5 + 6 + 6 + 7 + 7 + 8 + 8 + 9 + 9 +10 +10
= (1+9) + (1+9) + (2+8) + (2+8) + (3+7) + (3+7) + (4+6) + (4+6) + (5+5) + 10+10
= 10 + 10 +10 + 10 +10 +10 +10 +10 + 10 + 10 +10
= 10 x 11
= 110
Bài 1:
+) \(\dfrac{7}{8}\times y=\dfrac{3}{2}+\dfrac{6}{4}=3\)
\(y=3:\dfrac{7}{8}=\dfrac{24}{7}\)
+) \(\dfrac{1}{y}\times\left(\dfrac{2}{5}+\dfrac{1}{5}\right)=\dfrac{10}{3}\)
\(\dfrac{1}{y}=\dfrac{10}{3}:\dfrac{3}{5}=\dfrac{50}{9}\)
\(y=\dfrac{9}{50}\)
10 x 10 = 100
9 x 9 = 81
8 x 8 = 64
7 x 7 = 49
6 x 6 = 36
5 x 5 = 25
4 x 4 = 16
3 x 3 = 9
2 x 2 = 4
1 x 1 = 1
10 . 10 =102=100
9 . 9 =92=81
8 . 8 =82=64
7 . 7 =72=49
6 . 6 =62=36
5 . 5 =52=25
4 . 4 =42=16
3 . 3 =32=9
2 . 2 =22=4
1 . 1 =12=1
a: =>4/7<x<23/6
hay \(x\in\left\{1;2;3\right\}\)
b: =>19/10<x<27/5
hay \(x\in\left\{2;3;4;5\right\}\)
\(\dfrac{7}{10}+3:10+\dfrac{2}{5}+1:10\\ =\left(\dfrac{7}{10}+\dfrac{2}{5}\right)+\left(3:10+1:10\right)\\ =\dfrac{11}{10}+\left(3+1\right)\times\dfrac{1}{10}\\ =\dfrac{11}{10}+4\times\dfrac{1}{10}\\ =\dfrac{11}{10}+\dfrac{2}{5}\\ =\dfrac{3}{2}\)
\(\dfrac{7}{10}+3:10+\dfrac{2}{5}+1:10\\ =\dfrac{7}{10}+\dfrac{3}{10}+\dfrac{2}{5}+\dfrac{1}{10}\\ =\left(\dfrac{7}{10}+\dfrac{3}{10}\right)+\left(\dfrac{2}{5}+\dfrac{1}{10}\right)\\ =\dfrac{10}{10}+\left(\dfrac{4}{10}+\dfrac{5}{10}\right)=\dfrac{10}{10}+\dfrac{5}{10}=\dfrac{15}{10}=\dfrac{3}{2}\)
\(3+3+7+7+10+5+5\)\(5\)
\(=\left(3+7\right)+\left(3+7\right)+10+\left(5+5\right)\)
\(=10+10+10+10\)
\(=10.4\)
\(=40\)
\(nha^{ }\)
\(3+3+7+7+10+5+5\)
\(=\left(3+7\right)+\left(3+7\right)+\left(5+5\right)+10\)
\(=10+10+10+10\)
\(=40\)