5+6+7+8+9

=35

5+6+7+8+9+10

=45

a)4/7x(10/4+4/5)

=4/7x33/10=66/35

b)(17/35x35/17)x(11/5x25/11)

=1x5=5

xin 1 like( outo đúng nhé)

a: \(\frac{10}{4}\times\frac47+\frac47\times\frac45\)

\(=\frac47\times\frac52+\frac47\times\frac45\)

\(=\frac47\times\left(\frac52+\frac45\right)=\frac47\times\left(\frac{25}{10}+\frac{8}{10}\right)=\frac47\times\frac{33}{10}=\frac{132}{70}=\frac{66}{35}\)

b: \(\frac{11}{5}\times\frac{17}{35}\times\frac{25}{11}\times\frac{35}{17}\)

\(=\frac{11}{5}\times\frac{25}{11}\times\frac{17}{35}\times\frac{35}{17}\)

\(=\frac{11}{5}\times\frac{25}{11}=\frac{25}{5}=5\)

Đáp án :

1+2+3+...+20=210

~ hok tốt ~

= 210

NHA EM ( BẠN)

Thành gì

No,No,No

1+2+3+4+5+6+7+8+9+10+11+12+13+14+15+16+17+18+19+20+21=231

trả lời:

=231

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3 phút nha :>

1 phút

(1+2+3+4+5+6+7+8+9+10+11+12+13+14+15+16+17+18+19+20)*(21*4+6-84)=330

330 nha

1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9 + 10 + 11 + 12 + 13 + 14 + 15 + 16 + 17 + 18 + 19 + 20 + 21 + 22 + 23 + 24 + 25 + 26 + 27

=(1 + 19) + (2 +18) + (3 + 27) + (4 + 26) + (5 + 25) + (6 + 24) + (7 + 23) + (8 + 22) + (9 + 21) + (10 + 20) + (11 +19) + (12 + 18) + (13 + 17) + (14 + 16)

=20 + 20 + 30 + 30 + 30 + 30 + 30 + 30 + 30 + 30 + 30 + 30 + 30 + 15

=40 + 330 + 15

=381

Cứ lấy (đầu + cuối) nhân số số hạng rồi chia 2 là đc

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

=20x5

=100

19+1  +   17+3    +    15+5    +     13+7    +    11+9=20 nhan 5 =100. nhé