kb nha

kb nha

a,123456

b,37

nhớ tk mình nha.

đừng quên đó

các bn nhớ kb với tớ nhé

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)\(\frac{24}{x}\times\frac{1}{4}=\frac{2}{5}\)

\(\frac{24}{x}=\frac{2}{5}:\frac{1}{4}\)

\(\frac{24}{x}=\frac{8}{5}\)

\(x=24:\frac{8}{5}\)

\(x=15\)

X = 240

=8035

Số cần tìm là :

3568 + 4467 = 8035

ĐÁp số : 8035

\(\frac{1}{12}+\frac{1}{20}+\frac{1}{30}+...+\frac{1}{132}=\frac{1}{3\cdot4}+\frac{1}{4\cdot5}+\frac{1}{5\cdot6}+...+\frac{1}{11\cdot12}\)

\(=\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+...+\frac{1}{11}-\frac{1}{12}\)

\(=\frac{1}{3}-\frac{1}{12}=\frac{4}{12}-\frac{1}{12}=\frac{3}{12}=\frac{1}{4}\)

Chú ý: \(\cdot=\times\)

Đặt \(A=\frac{1}{12}+\frac{1}{20}+\frac{1}{30}+\frac{1}{42}+...+\frac{1}{132}\)

\(A=\frac{1}{3.4}+\frac{1}{4.5}+\frac{1}{5.6}+\frac{1}{6.7}+...+\frac{1}{11.12}\)

\(A=\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}+...+\frac{1}{11}-\frac{1}{12}\)

\(\Rightarrow A=\frac{1}{3}-\frac{1}{12}=\frac{1}{4}\)

20142013/20142012  = 20142012/20142011 nha Trương Phạm Bình An