tính nhanh
1/2 + 4/4 + 4/8 + 4/10 + 1/32 + 1/2
4/42 + 1/30 + 1/20 + 1/6 + 1/2
327 x 329 - 1
326 + 327 x 328
nhanh lên nhé tí nữa mình phải nộp rồi ai xong nhanh mình tik
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a) 25, 7 + 9, 48 + 14, 3
= ( 25, 7 + 14, 3 ) + 9, 48
= 40 + 9, 48
= 49, 48
b) 8, 24 + 3, 69 + 2, 31
= 8, 24 + ( 3, 69 + 2, 31 )
= 8, 24 + 6
= 14, 24
c) 8, 65 + 7, 6 + 1, 35 + 0, 4
= ( 8, 65 + 1, 35 ) + ( 7, 6 + 0, 4 )
= 10 + 8
= 18
d) 5, 92 + 0, 44 + 5, 56 + 4, 08
= ( 5, 92 + 4, 08 ) + ( 0, 44 + 5, 56 )
= 10 + 6
= 16
a 25,7+9,48+14,3
=40+9,48=49,48
b 8,24+3,69+2,31
6+8,2=14,2
c 8,65+7,6+1,35+0,4
10+8+1=19
d 5,92+0,44+5,56+4,08
=10+6=16
a)\(\frac{24}{x}\times\frac{1}{4}=\frac{2}{5}\)
\(\frac{24}{x}=\frac{2}{5}:\frac{1}{4}\)
\(\frac{24}{x}=\frac{8}{5}\)
\(x=24:\frac{8}{5}\)
\(x=15\)
\(\frac{1}{12}+\frac{1}{20}+\frac{1}{30}+...+\frac{1}{132}=\frac{1}{3\cdot4}+\frac{1}{4\cdot5}+\frac{1}{5\cdot6}+...+\frac{1}{11\cdot12}\)
\(=\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+...+\frac{1}{11}-\frac{1}{12}\)
\(=\frac{1}{3}-\frac{1}{12}=\frac{4}{12}-\frac{1}{12}=\frac{3}{12}=\frac{1}{4}\)
Chú ý: \(\cdot=\times\)
Đặt \(A=\frac{1}{12}+\frac{1}{20}+\frac{1}{30}+\frac{1}{42}+...+\frac{1}{132}\)
\(A=\frac{1}{3.4}+\frac{1}{4.5}+\frac{1}{5.6}+\frac{1}{6.7}+...+\frac{1}{11.12}\)
\(A=\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}+...+\frac{1}{11}-\frac{1}{12}\)
\(\Rightarrow A=\frac{1}{3}-\frac{1}{12}=\frac{1}{4}\)