-5,81 . 5/8 + 6,73 : (-1,6) - 1,54 : -8/5

= -5,81 . 5/8 + 6,73 : -8/5 - 1,54 : -8/5

= -5,81 .5/8 + 6,73 . -5/8 - 1,54 . -5/8

= (-5,81 - 6,73 + 1,54) . 5/8

= -11 . 5/8 = -55/8

1+1,3+1,6+.......+9,7+10

={10-1}:0,3+1=31

=1+1,3+...+10={10+1}x31:2=170,5

Ta có :

1,3 + 9,7 = 11

1,6 + 9,4 = 11

Có số số hạng :

( 10 - 1 ) : 0,3 + 1 = 31 ( số )

Trung bình cộng của dãy trên cũng là số ở giữa ( không có cặp ) :

( 10 + 1 ) : 2 = 5,5

Tổng trên :
( 31 - 1 ) : 2  x 11 + 5,5 = 170,5

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\(\left(24\%+\dfrac{3}{4}+0,76+25\%\right)\times\left(\dfrac{3}{\dfrac{5}{7}}+\dfrac{1}{\dfrac{8}{28}}\right)\)

\(=\left(0,24 +0,75+0,76+0,25\right)\times\left(4,2+10,5\right)\)

\(=\left[\left(0,24+0,76\right)+\left(0,75+0,25\right)\right]\times\left(4,2+10,5\right)\)

\(=\left[1+1\right]\times\left(4,2+10,5\right)\)

\(=2\times14,7=29,4\)

\(~HT~,#Ng\)

0,8 x 96+1,6 x 2+1,6 x 50

=0,8 x 2 x 48+1,6 x 2+1,6 x 50

=1,6 x 48+1,6 x 2+1,5 x 50

=1,6 x (48+2+50)

=1,6 x 100

=160

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

= 10 + 10 + 10 +10 +10 + 10 + 10 + 10 + 10

= 10 x 9

= 90

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

=10+10+10+10+10

=50

tổng quát: \(\frac{1}{n.\left(n+1\right)}=\frac{1}{n}-\frac{1}{n+1}\)

Ta có: \(\frac{1}{3.4}+\frac{1}{4.5}+\frac{1}{5.6}+\frac{1}{6.7}+\frac{1}{7.8}+\frac{1}{8.9}+\frac{1}{9.10}\)

\(=\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}+\frac{1}{7}-\frac{1}{8}+\frac{1}{8}-\frac{1}{9}+\frac{1}{9}-\frac{1}{10}\)

\(=\frac{1}{3}-\frac{1}{10}=\frac{10}{30}-\frac{3}{30}=\frac{7}{30}\)

Đặt S = 1 x 2 + 2 x 3 + ..... + 9 x 10

3S = 1 x 2 x (3-0) + 2 x 3 x (4 - 1) + ....... + 9 x 10 x (11 - 8)

3S = 1 x 2 x 3 + 2 x 3 x 4 - 1 x 2 x 3 + ......... + 9 x 10 x 11 - 8 x 9 x 10

3S = ( 1 x 2 x 3 -1 x 2 x 3) + ( 2 x 3 x4 - 2 x 3 x 4) + ..... + (8 x 9  x 10 - 8 x 9 x 10) + 9 x 10 x 11

3S = 9 x 10 x 11 = 990

S = 990 : 3 = 330