+1

(9+1)+(2+8)+(3+7)+(4+6)+10+5

(9+1) +(7+3)+(6+4) +(8+2)+(10+5)

=10+10+10+10+15

=55

\(\frac{9}{10}\)+\(\frac{7}{9}\)+\(\frac{5}{8}\)+\(\frac{3}{7}+\frac{3}{5}+\frac{2}{5}+\frac{4}{7}+\frac{3}{8}+\frac{2}{9}+\frac{1}{10}\)

\(=\left(\frac{9}{10}+\frac{1}{10}\right)+\left(\frac{7}{9}+\frac{2}{9}\right)+\left(\frac{5}{8}+\frac{3}{8}\right)\)\(+\left(\frac{3}{7}+\frac{4}{7}\right)+\left(\frac{3}{5}+\frac{2}{5}\right)\)

\(=1+1+1+1+1\)

\(=5\)

9/10 + 7/9 + 5/8 + 3/7 + 3/5 + 2/5 + 4/7 + 3/8 + 2/9 + 1/10

= ( 9/10 + 1/10 ) + ( 7/9 + 2/9 ) + ( 5/8 + 3/8 ) + ( 3/7 + 4/7 ) + ( 3/5 + 2/5 )

= 1 + 1 + 1 + 1 + 1

= 5

= (9/10+ 1/10 )+(7/9 + 2/9)+( 5/8 +3/8)+(3/5 +2/5)

=1+1+1+1=4

55 nha bn 

55 na bạn 

1+2+3+4+5+6+7+8+9+10=55 nha bạn

= (1 + 10) + (9 +2)+(8+3)+(7+4)+(5+6)

= 11 +11 +11 +11+11

=55

1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9 + 10 

=(1+9)+(2+8)+(3+7)+(4+6)+5+10

=10+10+10+10+5+10

=55

\(1+2+3+4+5+6+7+8+9+10\)

\(=(1+9)+(2+8)+(3+7)+(4+6)+10+5\)

\(=10+10+10+10+10+5\)

\(=10\times4+5\)

\(=55\)

Chúc bạn học tốt

(56-49-7)(1+2+3+4+5+6+7+8+9+10)=0x(1+2+3+4+5+6+7+8+9+10)=0

    56 -49 - 7 = 0 

0 nhân số nào cũng bằng 0

(56-7x7-7)x(1+2+3+4+5+6+7+8+9+10)

= (56-49-7)x(1+2+3+4+5+6+7+8+9+10)

= 0 x (1+2+3+4+5+6+7+8+9+10)

=0

\(\frac{9}{10}+\frac{7}{9}+\frac{5}{8}+\frac{3}{7}+\frac{3}{5}+\frac{2}{5}+\frac{4}{7}+\frac{3}{8}+\frac{2}{9}+\frac{1}{10}\)

= \(\left(\frac{9}{10}+\frac{1}{10}\right)+\left(\frac{7}{9}+\frac{2}{9}\right)+\left(\frac{5}{8}+\frac{3}{8}\right)+\left(\frac{3}{7}+\frac{4}{7}\right)+\left(\frac{3}{5}+\frac{2}{5}\right)\)

= \(\frac{10}{10}+\frac{9}{9}+\frac{8}{8}+\frac{7}{7}+\frac{5}{5}\)

= \(1+1+1+1+1\)

= \(1\times5\)

= \(5\)

Gọi A là tổng của 9/10 + 7/9 + 5/8 + 3/7 + 3/5 + 2/5 + 4/7 + 3/8 + 2/9 + 1/10, ta có :

A = 9/10 + 7/9 + 5/8 + 3/7 + 3/5 + 2/5 + 4/7 + 3/8 + 2/9 + 1/10

A = (9/10 + 1/10) + (7/9 + 2/9) + (5/8 + 3/8) + (3/7 + 4/7) + (3/5 + 2/5)

A = 1 + 1 + 1 + 1 + 1

A = 5

Ta có \(\frac{9}{10}+\frac{7}{9}+\frac{5}{8}+\frac{3}{7}+\frac{3}{5}+\frac{2}{5}+\frac{4}{7}+\frac{3}{8}+\frac{2}{9}+\frac{1}{10}\)

\(=\left(\frac{9}{10}+\frac{1}{10}\right)+\left(\frac{7}{9}+\frac{2}{9}\right)+\left(\frac{3}{8}+\frac{5}{8}\right)+\left(\frac{3}{7}+\frac{4}{7}\right)+\left(\frac{2}{5}+\frac{3}{5}\right)\)

\(=1+1+1+1+1\)

\(=5\)

\(\frac{9}{10}+\frac{7}{9}+\frac{5}{8}+\frac{3}{7}+\frac{3}{5}+\frac{2}{5}+\frac{4}{7}+\frac{3}{8}+\frac{2}{9}+\frac{1}{10}\)\(=\frac{9}{10}+\frac{1}{10}+\frac{7}{9}+\frac{2}{9}+\frac{5}{8}+\frac{3}{8}+\frac{3}{7}+\frac{4}{7}+\frac{3}{5}+\frac{2}{5}\)

\(=\left[\frac{9}{10}+\frac{1}{10}\right]+\left[\frac{7}{9}+\frac{2}{9}\right]+\left[\frac{5}{8}+\frac{3}{8}\right]+\left[\frac{3}{7}+\frac{4}{7}\right]+\left[\frac{3}{5}+\frac{2}{5}\right]\)

\(=1+1+1+1+1\)

   \(=5\)

\(\frac{9}{10}+\frac{7}{9}+\frac{5}{8}+\frac{3}{7}+\frac{3}{5}+\frac{2}{5}+\frac{4}{7}+\frac{3}{8}+\frac{2}{9}+\frac{1}{10}\)

= \(\left(\frac{9}{10}+\frac{1}{10}\right)+\left(\frac{7}{9}+\frac{2}{9}\right)+\left(\frac{5}{8}+\frac{3}{8}\right)+\left(\frac{3}{7}+\frac{4}{7}\right)+\left(\frac{3}{5}+\frac{2}{5}\right)\)

= 1 + 1 + 1 + 1 + 1

= 5

=1+1+1+1+1

=5

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