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tính như bình thường nha bạn. Có những câu đề bài là tính thuận tiện mà tính thường mk đã gặp nhiều rồi
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= 5.8m2 x 1 + 5.8cm2 x3 + 5.8cm2 x 1
= 5.8cm2 x ( 1+ 3+ 1)
=5.8cm2 x 5
=29 cm2
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\(\left(\dfrac{3}{2.5}+\dfrac{3}{5.8}+...+\dfrac{3}{17.20}\right).x=\dfrac{45}{23}\)
\(\left(\dfrac{1}{2}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{8}+....+\dfrac{1}{17}-\dfrac{1}{20}\right).x=\dfrac{45}{23}\)
\(\left(\dfrac{1}{2}-\dfrac{1}{20}\right).x=\dfrac{45}{23}\)
\(\dfrac{9}{20}\cdot x=\dfrac{45}{23}\)
\(x=\dfrac{45}{23}:\dfrac{9}{20}\)
\(x=\dfrac{100}{23}\)
\(\left(\dfrac{3}{2.5}+\dfrac{3}{5.8}+...+\dfrac{1}{17.20}\right)x=\dfrac{45}{23}\Leftrightarrow\left(\dfrac{1}{2}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{8}+...+\dfrac{1}{17}-\dfrac{1}{20}\right)x=\dfrac{45}{23}\)\(\Leftrightarrow\left(\dfrac{1}{2}-\dfrac{1}{20}\right)x=\dfrac{45}{23}\)
\(\Rightarrow\dfrac{9}{20}.x=\dfrac{45}{23}\)
\(\Rightarrow x=\dfrac{100}{23}\)
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253 x 75 - 161 x 37 + 253 x 25 - 161 x 63
= 253 x (75 + 25) - 161 x (37 + 63)
=253 x 100 - 161 x 100
=23500 - 16100
=37400
100 x 47 - 12 x 3,5 - 5,8 : 0,1
=4700 - 42 - 58
=4700 - (42 + 58)
=4700 - 100
=4600
=5,8(1+3+5+1)=58
=5.8 x (3+5)
=5.8 x 8
=29