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y + y + y + y x 2 = 1.285
y x (1 + 1 + 1 + 2) = 1.285
y x 5 = 1.285
y = 1.285 : 5
y = 257
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Bài 1:
+) \(\dfrac{7}{8}\times y=\dfrac{3}{2}+\dfrac{6}{4}=3\)
\(y=3:\dfrac{7}{8}=\dfrac{24}{7}\)
+) \(\dfrac{1}{y}\times\left(\dfrac{2}{5}+\dfrac{1}{5}\right)=\dfrac{10}{3}\)
\(\dfrac{1}{y}=\dfrac{10}{3}:\dfrac{3}{5}=\dfrac{50}{9}\)
\(y=\dfrac{9}{50}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
a. x = 1+ 2+ 3+ 4 + 5 + 6 + 7 + 8 + 9 +10
= (1 +10) + (2+9) + ( 3 +8 ) + (4 + 7 ) + (5 + 6)
= 11 +11 + 11+ 11 +11
= 11 x 5
= 55
b. y = 2 + 4 + 6 + 8 + 10 + 12 + 14 + 16 + 18 + 20
= (2+20) + (4 + 18) + (6 + 16) +(8 + 14) + (10 +12)
= 22 + 22 + 22 +22 + 22
= 22 x 5
= 110
![](https://rs.olm.vn/images/avt/0.png?1311)
3 x 6 + 3 x 70 + 24 x 3
= 3 x (6 + 70 + 24)
= 3 x 100
= 300
3 x 6 + 3 x 70 + 24 x 3
= 3 x (6 + 70 + 24)
= 3 x 100 = 300
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\(\text{A) 38 x 10 = 380}\)
\(\text{B) 20 x 6 = 120}\)
\(\text{C) 51 x 5 = 255}\)
bằng 1