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1/10+2/9+3/8+4/7+5/6+1/6+3/7+5/8+7/9+9/10
=(1/10+9/10)+(2/9+7/9)+(3/8+5/8)+(4/7+3/7)+(5/6+1/6)
=1+1+1+1+1
=5
![](https://rs.olm.vn/images/avt/0.png?1311)
Bài 7:
Số phần kẹo Hùng đã cho Hà và Hồng là:
\(\dfrac{2}{7}+\dfrac{1}{7}=\dfrac{3}{7}\left(phần\right)\)
Hùng còn lại số phần của gói kẹo là:
\(\dfrac{6}{7}-\dfrac{3}{7}=\dfrac{3}{7}\left(phần\right)\)
1:
2 3/4
5 6/5
3 3/9
7 6/8
2:
1/3 + 2/3 + (3/4 + 1/4) = 2
=2
= 4 5/10
![](https://rs.olm.vn/images/avt/0.png?1311)
Ta có
\(\frac{1}{10}+\frac{2}{10}+\frac{3}{10}+\frac{4}{10}+\frac{5}{10}+\frac{6}{10}+\frac{7}{10}+\frac{8}{10}+\frac{9}{10}\)
\(=\frac{1+2+3+4+5+6+7+8+9}{10}\)
\(=\frac{\left(1+9\right)+\left(2+8\right)+\left(3+7\right)+\left(4+6\right)+5}{10}=\frac{10.4+5}{10}=\frac{45}{10}=\frac{9}{2}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(=\dfrac{1+2+3+4+5+6+7+8+9}{10}\\ =\dfrac{\left(1+9\right)+\left(2+8\right)+\left(3+7\right)+\left(4+6\right)+5}{10}\\ =\dfrac{10+10+10+10+5}{10}=\dfrac{45}{10}=\dfrac{9}{2}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
b)1/2*2/3*3/4*4/5*5/6*6/7*7/8*8/9*9/10
=1x2x3x4x5x6x7x8x9
2x3x4x5x6x7x8x9x10
= 1
10
![](https://rs.olm.vn/images/avt/0.png?1311)
Ta có : \(\dfrac{1}{6}>\dfrac{1}{10}\)
\(\dfrac{1}{7}>\dfrac{1}{10}\)
\(\dfrac{1}{8}>\dfrac{1}{10}\)
\(\dfrac{1}{9}>\dfrac{1}{10}\)
\(\dfrac{1}{10}=\dfrac{1}{10}\)
Cộng tất cả các vế ( phải theo phải ) ( trái theo trái ta được )
\(\dfrac{1}{6}+\dfrac{1}{7}+\dfrac{1}{8}+\dfrac{1}{9}+\dfrac{1}{10}>\dfrac{1}{10}+\dfrac{1}{10}+\dfrac{1}{10}+\dfrac{1}{10}+\dfrac{1}{10}\)
\(\Rightarrow\dfrac{1}{6}+\dfrac{1}{7}+\dfrac{1}{8}+\dfrac{1}{9}+\dfrac{1}{10}>\dfrac{5}{10}=\dfrac{1}{2}\)
Ta có:
\(\dfrac{1}{6}>\dfrac{1}{10}\)
\(\dfrac{1}{7}>\dfrac{1}{10}\)
\(\dfrac{1}{8}>\dfrac{1}{10}\)
\(\dfrac{1}{9}>\dfrac{1}{10}\)
\(\dfrac{1}{10}=\dfrac{1}{10}\)
Do đó ta có:
\(\dfrac{1}{6}+\dfrac{1}{7}+\dfrac{1}{8}+\dfrac{1}{9}+\dfrac{1}{10}>\dfrac{1}{10}+\dfrac{1}{10}+\dfrac{1}{10}+\dfrac{1}{10}+\dfrac{1}{10}\)
\(\Rightarrow\dfrac{1}{6}+\dfrac{1}{7}+\dfrac{1}{8}+\dfrac{1}{9}+\dfrac{1}{10}>\dfrac{1}{10}\times5\)
\(\Rightarrow\dfrac{1}{6}+\dfrac{1}{7}+\dfrac{1}{8}+\dfrac{1}{9}+\dfrac{1}{10}>\dfrac{5}{10}=\dfrac{1}{2}\)
Vậy \(\dfrac{1}{6}+\dfrac{1}{7}+\dfrac{1}{8}+\dfrac{1}{9}+\dfrac{1}{10}>\dfrac{1}{2}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
Câu 1:
A = (a x 7 + a x 8 - a x 15) : (1 + 2 + 3 + ........ + 10)
A = a x(7+8-15) : (1+2+3+...+10)
A = a x 0 : (1+2+3+...+10)
A = 0: (1+2+3+4+...+10)
A = 0
Câu 2:
B = (18 - 9 x 2) x (2 + 4 + 6 + 8 + 10)
B = (18 - 18) x (2+4+6+8+10)
B = 0 x ( 2 + 4 + 6 + 8 +10)
B = 0
Giáng sinh vui vẻ nhé !
A = {a x (7 + 8 - 15 ) }: (1+2+3+4+........+10)
= {a x 0 } : (1+2+3+4+........+10)
= 0 : (1+2+3+4+........+10)
= 0
đây câu A đây
![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
1 + 2 + 8 + 9 + 1 + 2 + 8 + 9 + 10 + 10
= (1 + 9) + (1 + 9) + (2 + 8) + (2 + 8) + 10 + 10
= 10 + 10 + 10 + 10 + 10 + 10
= 60
=1+9+2+8+1+9+2+8+10+10
=10+10+10+10+10+10
=10x6
=60
k mk nha mk k lại!