A = 1 + 3 + 5 + 7 +...+ 19

Dãy số trên là dãy số cách đều với khoảng cách là:  3 - 1 = 2

Số số hạng của dãy số trên là: ( 19 - 1): 2 + 1  = 10 

A = ( 19 + 1) \(\times\) 10 : 2 = 100

  52 - 42 + 37 + 28 - 38 + 63

= ( 52 + 28) - ( 42 + 38) + ( 37 + 63)

= 80 - 80 + 100

= 100 

 1 + 3 + 5 + 7 + 9+ 11 + 13 + 15 + 17 + 19

= (1+ 19) + (3 + 17) + (5 + 15) + (7 + 13) + (9 + 11)

= 20 + 20 + 20 + 20 + 20

= 100

 52 - 42 + 37 + 28 - 38 + 63

= (52 + 28) - ( 42 + 38) + (37 + 63)

= 80 - 80 + 100

= 100

Tick cho mình nhé!

A = 1 + 3 + 5 + ... + 17 + 19

Số số hạng:

(19 - 1) : 2 + 1 = 10 (số hạng)

A = (19 + 1) × 10 : 2 = 100

------------------

52 - 42 + 37 + 28 - 38 + 63

= (37 + 63) + (52 + 28) - (42 + 38)

= 100 + 80 - 80

= 100 + 0

= 100

\(\begin{array}{*{20}{c}}{ + \begin{array}{*{20}{c}}{38}\\{52}\end{array}}\\\hline{\,\,\,90}\end{array}\)                                     \(\begin{array}{*{20}{c}}{ + \begin{array}{*{20}{c}}{15}\\{15}\end{array}}\\\hline{\,\,\,30}\end{array}\)

\(\begin{array}{*{20}{c}}{ + \begin{array}{*{20}{c}}{67}\\{17}\end{array}}\\\hline{\,\,\,84}\end{array}\)                                     \(\begin{array}{*{20}{c}}{ + \begin{array}{*{20}{c}}{72}\\{19}\end{array}}\\\hline{\,\,\,91}\end{array}\)

a) 52 – 42 + 37 – 28 + 38 + 63 = (52 – 42) + (37 + 63) + (38 – 28) = 10 + 100 + 10 =  120

b) 130 + 35.19 – 9.70 – 30

= (35.19 – 9.70) + (130 – 30) = (35.19 – 9.35.2) + 100 = 35.(19 – 18) + 100 = 35 + 100 = 135

c) (11 + 13 + 15 + … + 19).(6.8 – 48) = (11+13+15+…+19).0 = 0

d) (72 – 8.9):(20+22+24 – 19 +21+23) = 0:(20+22+24 – 19 +21+23) = 0

a: \(=\dfrac{21}{11}+\dfrac{12}{11}+\left(-\dfrac{9}{19}-\dfrac{3}{19}-\dfrac{6}{19}\right)=3-\dfrac{18}{19}=\dfrac{39}{19}\)

b: \(=\dfrac{2}{3}+\dfrac{4}{3}+\dfrac{3}{4}+\dfrac{7}{4}+\dfrac{4}{5}+\dfrac{16}{5}=2+4+\dfrac{5}{2}=6+\dfrac{5}{2}=\dfrac{17}{2}\)

Bài 1: 

a: -8/12<0<-3/-4

b: -56/24<0<7/3

c: 4/25<1<15/13

=>-4/25>-15/13

Bài 2: 

a: =-60/45=-4/3

b: =4/15-3/2-8/5=8/30-45/30-48/30=-85/30=-17/6

a,(815+185)-(23+77)

=1000-100=900

b,(2496+7504)+(5347+4653)+3145

=10000+               10000          +3145

=23146

c,(1+19)+(3+17)+(5+15)+(7+13)+(9+11)

=20+20+20+20+20=100

d,(52+28)+(37+63)-(42+38)

=80+100-80=100

mk nha

a,(815+185)-(23+77)

=1000-100=900

b,(2496+7504)+(5347+4653)+3145

=10000+               10000          +3145

=23146

c,(1+19)+(3+17)+(5+15)+(7+13)+(9+11)

=20+20+20+20+20=100

d,(52+28)+(37+63)-(42+38)

=80+100-80=100

mk nha

Tính nhanh:

a. 815 - 23 - 77 + 185

= (815+185)-(23+77)

=1000 - 100

= 900

b. 3145 + 2496 + 5347 + 7504 + 4653

=3145+(2496+7504)+(5347+4653)

= 3145+10 000 + 10 000

= 3145 + 20 000

= 23 145

c. 1 + 3 + 5 + 7 + 9+ 11 + 13 + 15 + 17 + 19

=(1+19)+(3+17)+(5+15)+(7+13)+(9+11)

= 20  +   20    +   20 + 20 + 20

= 20 × 5 

= 100

d. 52 - 42 + 37 + 28 - 38 + 63

= ( 52 + 28 ) - ( 42 + 38 ) + ( 37 + 63 )

=  80  -  80  + 100

= 0 + 100

= 100 

X = 7 ; 8 .

#HT#

Bạn tự làm bài nếu bạn không tính được thì bạn hỏi cô hay thầy đấy nha bạn,chúc bạn học giỏi nha:

a, \(\frac{39}{19}\)

b, \(8.5\)hay \(\frac{17}{2}\)

c, \(\frac{1277}{4186}\)

Bấm máy tính là được ^_^

\(.\)

cảm ơn bn nha Đặng Huy Hùng

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

\(=\frac{1}{3}\left(\frac{4}{5}+\frac{6}{5}\right)\)

\(=\frac{1}{3}.2\)

\(=\frac{2}{3}\)

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

\(=\frac{1}{3}.\left(\frac{4}{5}+\frac{6}{5}-1\right)\)

\(=\frac{1}{3}.\left(\frac{4}{5}+\frac{6}{5}-\frac{5}{5}\right)\)

\(=\frac{1}{3}.1\)

\(=\frac{1}{3}\)

\(2)\)\(\frac{3}{7}.\frac{9}{26}-\frac{1}{14}.\frac{1}{13}\)

\(=\frac{1}{7}.\frac{27}{26}-\frac{1}{7}.\frac{1}{26}\)

\(=\left(\frac{27}{26}-\frac{1}{26}\right).\frac{1}{7}\)

\(=1.\frac{1}{7}\)

\(=\frac{1}{7}\)

\(3)\)\(15\left(\frac{1}{5}-\frac{7}{15}+\frac{17}{3}\right)\)

\(=3-7+85\)

\(=81\)

\(4)\)\(38\left(2\frac{1}{19}-5\frac{7}{38}\right)\)

\(=38\left(\frac{39}{19}-\frac{197}{38}\right)\)

\(=78-197\)

\(=-119\)

\(5)\)\(75\left(\frac{-4}{25}+7\frac{1}{15}-5\frac{7}{75}\right)\)

\(=75\left(\frac{-4}{25}+\frac{106}{15}-\frac{382}{75}\right)\)

\(=-12+530-382\)

\(=136\)

Ddaeng

1, \(\frac{1}{3}.\frac{4}{5}+\frac{1}{3}.\frac{6}{5}-\frac{1}{3}\)

\(=\frac{1}{3}.\left(\frac{4}{5}+\frac{6}{5}\right)-\frac{1}{3}\)

\(=\frac{1}{3}.2-\frac{1}{3}\)

\(=\frac{2}{3}-\frac{1}{3}\)

\(=\frac{1}{3}\)

2, \(\frac{3}{7}.\frac{9}{26}-\frac{1}{14}.\frac{1}{13}\)

\(=\frac{1}{7}.3.\frac{9}{26}-\frac{1}{7}.\frac{1}{2}.\frac{1}{13}\)

\(=\frac{1}{7}.\frac{27}{26}-\frac{1}{7}.\frac{1}{26}\)

\(=\frac{1}{7}.\left(\frac{27}{26}-\frac{1}{26}\right)\)

\(=\frac{1}{7}.1\)

\(=\frac{1}{7}\)

3, \(15.\left(\frac{1}{5}-\frac{7}{15}+\frac{17}{3}\right)\)

\(=15.\frac{1}{5}-15.\frac{7}{15}+15.\frac{17}{3}\)

\(=3-7+85\)

\(=81\)

4, \(38.\left(2\frac{1}{19}+5\frac{7}{38}\right)\)

\(=38.\left(\frac{39}{19}+\frac{197}{38}\right)\)

\(=38.\frac{39}{19}+38.\frac{197}{38}\)

\(=78+197\)

\(=275\)

5, \(75.\left(\frac{-4}{25}+7\frac{1}{15}-5\frac{7}{75}\right)\)

\(=75.\left(\frac{-4}{25}+\frac{106}{15}-\frac{382}{75}\right)\)

\(=75.\frac{-4}{25}+75.\frac{106}{15}-75.\frac{382}{75}\)

\(=-12+530-382\)

\(=136\)