a) Xét tổng 1 + 6 + 11 + ........ + 46 

Số số hạng là :

 (46 - 1) : 5 + 1 = 10 (số)

Vậy 1 + 6 + 11 + ........ + 46 + 5 = (46 + 1) . 10 : 2 + 5 = 240

43/30

1/16

10/21

5/3

43/30

1/16

10/21

5/3

Cần chi tiết hum bẹn

có nha

a) 1-3+5-7+9-12+15-18

= (1+ 9) - (3+7) + (5+15) - (12+18) 

= 10 - 10 + 20 - 30 = -10.

b) (-2)+5-7+9-11+13-15+19-21

= 5 - 11 - 2 -2 = 5 - (11+2+2)

= 5 - 15 = -10 

Bài 1: 

a) Ta có: 1-3+5-7+9-12+15-18

=(1+9)-(3+7)+(5+15)-(12+18)

=10-10+20-30

=-10

b) Ta có: \(\left(-2\right)+5-7+9-11+13-15+19-21\)

\(=3+2+2+4-21\)

\(=5+6-21\)

=11-21=-10

`4/7+4`

`=4/7+4/1`

`=4/7+28/7`

`=32/7`

__

`3+6/11`

`=33/11+6/11`

`=39/11`

__

`3-5/7`

`=3/1-5/7`

`=21/7-5/7`

`=16/7`

__

`21/9-2`

`=21/9-18/9`

`=3/9`

`=1/3`

__

`15/24+2`

`=15/24+48/24`

`=63/24`

`=21/16`

__

`63/45-20/25`

`=63/45-4/5`

`=63/45-36/45`

`=27/45`

`=9/15`

__

`3/4-2/8`

`=3/4-1/4`

`=2/4`

__

`6/7-5/8`

`=48/56-35/56`

`=13/56`

__

`37/45-5/9`

`=37/45-25/45`

`=12/45`

`=4/15`

__

`46/39-11/13`

`=46/39-33/39`

`=13/39`

`=1/2`

__

`5/12+3/4+1/3`

`=5/12+9/12+4/12`

`=14/12+4/12`

`=18/12`

`=3/2`

__

`1/2+3/7+11/14`

`=7/14+6/14+11/14`

`=13/14+11/14`

`=24/14`

`=12/7`

__

`7/10-(1/5+1/4)`

`=7/10-(4/20+5/20)`

`=7/10-9/20`

`=14/20-9/20`

`=5/20`

`=1/4`

__

`15/4-2/3-3/4`

`=(15/4-3/4)-2/3`

`=12/4-2/3`

`=3-2/3`

`=9/3-2/3`

`=7/3`

a: \(\dfrac{7}{4}-\dfrac{11}{8}+\dfrac{1}{2}\)

\(=\dfrac{14-11+4}{8}\)

\(=\dfrac{7}{8}\)

b: \(\dfrac{3}{16}+\dfrac{7}{30}\cdot\dfrac{40}{36}\)

\(=\dfrac{3}{16}+\dfrac{7}{36}\cdot\dfrac{40}{30}\)

\(=\dfrac{3}{16}+\dfrac{7}{36}\cdot\dfrac{4}{3}\)

\(=\dfrac{3}{16}+\dfrac{7}{27}=\dfrac{81+112}{432}=\dfrac{193}{432}\)

c: \(\left(\dfrac{9}{2}-\dfrac{15}{4}\right):\dfrac{21}{12}\)

\(=\left(\dfrac{18}{4}-\dfrac{15}{4}\right):\dfrac{7}{4}\)

\(=\dfrac{3}{4}\cdot\dfrac{4}{7}=\dfrac{3}{7}\)