Question

( x+1) + ( x +2)+ ...........( x +17) + ( x +18) + ( x +19) + ( x +19) + ( x +20) = 4210

Answer 1

( x+1) + ( x +2)+ ...........( x +17) + ( x +18) + ( x +19) + ( x +19) + ( x +20) = 4210

(x+x+x+x+...+x+x+x) + (1+2+3+4+...+18+19+19+20)= 4210

21* x + (1+20):2 x 20 + 19 = 4210

21 * x + 229 = 4210

x = (4210 - 229) : 21 = 1327/7

Answer 2

=>20x+(20+1)*20/2=4210

=>20x+210=4210

=>20x=4000

=>x=200