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7
Đổi 16m2=160000cm2
Vậy cần \(160000:\left(50\times50\right)=64\left(viên\right)\left(D\right)\)
Đổi 16m2= 1600dm2
Diện tích viên gạch là:
50x50=2500(cm2)=25dm2
Vậy cần ít nhất số ciên gạch là:
1600:25=64(viên)
\(\Rightarrow\)Chọn D. 64 viên gạch
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a. -20+5=-15
b. 7
c. 35 + (-4)= 31
d. -129-37+29-63= -100-100 = -200
e. 217 -315-117+215 =100-100=0
f. 15:(-3)+24:2 = -5 + 12 = 7
g. (-5).(-7)-3.(14)= 35 - 42 = -7
H. (-15)x(-129+29) = -15 x -100 =1500
i. 13 x (-125+25) =13 x -100 = -1300
k. 37(-135+35) = 37 x -100 = -3700
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\(=\dfrac{10}{17}-\dfrac{5}{3}+7-\dfrac{8}{13}+\dfrac{11}{25}\)
\(=\dfrac{30}{51}-\dfrac{85}{51}+\dfrac{175}{25}+\dfrac{11}{25}-\dfrac{8}{13}\)
\(=\dfrac{-55}{51}+\dfrac{186}{25}-\dfrac{8}{13}\)
\(=\dfrac{-55\cdot325+186\cdot663-8\cdot1275}{16575}=\dfrac{95243}{16575}\)
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a: Ta có: \(\dfrac{n\left(n+1\right)}{2}=231\)
\(\Leftrightarrow n^2+n-462=0\)
\(\Leftrightarrow n^2+22n-21n-462=0\)
\(\Leftrightarrow\left(n+22\right)\left(n-21\right)=0\)
\(\Leftrightarrow n=21\)
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a ) 13/20
B)
C..........................................................
minh dang tính
d)\(\frac{15^{20}.9^{10}}{27^{12}.25^{10}}\)= \(\frac{\left(3.5\right)^{20}.\left(3^2\right)^{10}}{\left(3^3\right)^{12}.\left(5^2\right)^{10}}\)=\(\frac{3^{20}.5^{20}.3^{20}}{3^{36}.5^{20}}\)=\(\frac{3^{40}.5^{20}}{3^{36}.5^{20}}\)= 34 = 81