tính nhanh: a,2011 + 2011 + 2011 + 2011 - 2008 x 4
b, 72 x 55 + 216 x 15
c, 250 x 755-161x37+253 x25-161x 63/100 x 47 - 12x 3,5- 5,8 : 0,1
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a) 100 - 99 + 98 -97 + 96 -95 +...+ 4-3 + 2
= (100 - 99) + (98 -97) + (96 - 95) +...+ (4-3) +2 (gồm 49 cặp và 1 số hạng)
= 1+1+1+....+1 +2
= 49 x 1 + 2 = 51
b) 100 - 5-...-5 - 5 (20 số 5)
= 100 - 20 x 5 = 0
c) 99 - 9 - 9 -... - 9 -9 (11 số 9)
=99 - 11 x 9 = 0
d) 2011 + 2011+2011+2011 - 2008 x 4
= 2011 x 4 - 2008 x 4
= 4 x (2011 - 2008)
= 4 x 3
=12
a. 1⋅2⋅3+2⋅4⋅6+3⋅6⋅9+4⋅8⋅12
= 6+2⋅4⋅6+3⋅6⋅9+4⋅8⋅12
= 6+48+3⋅6⋅9+4⋅8⋅12
= 6+48+162+4⋅8⋅12
= 6+48+162+384
= 600
b . Ta có \(A=\frac{2010+2011}{2011+2012}=\frac{2010}{2011+2012}+\frac{2011}{2011+2012}.\)
Ta có : \(\frac{2010}{2011+2012}< \frac{2010}{2011}\) và \(\frac{2011}{2011+2012}< \frac{2011}{2012}\)
=> \(\frac{2010+2011}{2011+2012}< \frac{2010}{2011}+\frac{2011}{2012}\)
=> A < B
a, 2010 x 3+ 2010 x 6 + 2010
= 2010 x ( 3 + 6 + 1)
= 2010 x 10
= 20100
b, 2011 x 89 + 10 x 2011 + 2011
= 2011 x (89 + 10 + 1)
= 2011 x 100
= 201100
a, 2011 x 3+ 2011 x 6 + 2011
= 2011 x ( 3+6+1)
= 2011 x 10
= 20110
b, 2010 x 89 + 10 x 2010 + 2010
= 2010 x (89+10+1)
= 2010 x 100
= 201000
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
Ta có :
\(A=\frac{2012.14+1997+2010.2011}{2011.5+2011.1008+1012.2011}\)
\(\Rightarrow A=\frac{\left(2011+1\right).14+1997+2010.2011}{2011.\left(5+1008+1012\right)}\)
\(\Rightarrow A=\frac{2011.14+14+1997+2010.2011}{2011.2025}\)
\(\Rightarrow A=\frac{2011.14+2011+2010.2011}{2011.2025}\)
\(\Rightarrow A=\frac{2011.\left(14+1+2011\right)}{2011.2025}\)
\(\Rightarrow A=\frac{2011.25}{2011.25}\)
\(\Rightarrow A=1\) ( tử số = mẫu số )
Vậy \(A=1\)
~ Ủng hộ nhé
\(\left(x-2011\right)\left(\frac{1}{12}+\frac{1}{20}+\frac{1}{30}+\frac{1}{42}+\frac{1}{56}+\frac{1}{72}\right)=\frac{16}{9}\)
\(\left(x-2011\right)\cdot\frac{2}{9}=\frac{16}{9}\)
\(x-2011=8\)
\(x=2019\)
\(\frac{x-2011}{12}+\frac{x-2011}{20}+\frac{x-2011}{30}+\frac{x-2011}{42}+\frac{x-2011}{56}+\frac{x-2011}{72}=\frac{16}{9}\)
\(\left(x-2011\right)\left(\frac{1}{12}+\frac{1}{20}+\frac{1}{30}+\frac{1}{42}+\frac{1}{56}+\frac{1}{72}\right)=\frac{16}{9}\)
\(\left(x-2011\right)\left(\frac{1}{3.4}+\frac{1}{4.5}+\frac{1}{5.6}+\frac{1}{6.7}+\frac{1}{7.8}+\frac{1}{8.9}\right)=\frac{16}{9}\)
\(\left(x-2011\right)\left(\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+...+\frac{1}{8}-\frac{1}{9}\right)=\frac{16}{9}\)
\(\left(x-2011\right)\left(\frac{1}{3}-\frac{1}{9}\right)=\frac{16}{9}\)
\(\left(x-2011\right)\frac{2}{9}=\frac{16}{9}\)
\(x-2011=8\Rightarrow x=2019\)
a) 2011 + 2011 + 2011 + 2011 - 2008 x 4
= 2011 + 2011 + 2011 + 2011 - 8032
= 12
b) 72 x 55 + 216 x 15
= 3960 + 216 x 15
= 3960 + 3240
= 7200
c) 250 x 755 - 161 x 37 + 253 x 25 - 161 x \(\dfrac{63}{100}\) x 47 - 12 x 3,5 - 5,8 : 0,1
= \(\dfrac{18425079}{100}\)