Question

Answer 1

a/

$x+(x+1)+(x+2)+...+(x+2010)=2029099$

$\underbrace{(x+x+...+x)}_{2011}+(1+2+3+...+2010)=2029099$
$x\times 2011+2010\times 2011:2=2029099$

$x\times 2011+2021055=2029099$

$x\times 2011=8044$

$x=8044:2011=4$

Answer 2

b/

$2+4+6+8+...+2x=210$

Số số hạng của tổng: $(2x-2):2+1=x$

Vậy:

$2+4+6+8....+2x=210$

$\Rightarrow (2x+2)\times x:2=210$

$(x+1)\times x=210=14\times 15$

$\Rightarrow x=14$

Answer 3

c/

$(x+1)+(x+2)+(x+3)+...+(x+100)=205550$

$\underbrace{(x+x+....+x)}_{100}+(1+2+3...+100)=205550$

$x\times 100+100\times 101:2=205550$

$x\times 100+5050=205550$

$x\times 100=200500$

$x=200500:100$

$x=2005$

Answer 4

d/

$x+(x+1)+(x+2)+....+(x+30)=1240$

$\underbrace{(x+x+...+x)}_{31}+(1+2+...+30)=1240$

$x\times 31+30\times 31:2=1240$

$x\times 31+465=1240$

$x\times 31=775$

$x=775:31$

$x=25$