Question

(x +1) + (x + 2) + ( x + 3) + .....+ ( x + 9) +( x + 10) = 240

Answer 1

Ta có: ( x + 1 ) + ( x + 2 ) + ( x + 3 ) + .... + ( x + 9 ) + ( x + 10 ) = 240

<=> ( x + x + x + ...+ x ) + ( 1 + 2 + 3 + ... +10 ) = 240 

<=> 10x + 55 = 240

=> 55 + 10x = 240

=> 10x = 240 - 55

=> 10x = 185 

=>  x = 185 : 10 = 18,5

Vậy x = 18.5

Answer 2

(x +1) + (x + 2) + ( x + 3) + .....+ ( x + 9) +( x + 10) = 240

x * 10 + ( 1 + 2 +... + 10 ) = 240

x * 10 + \(\frac{10.11}{2}\)=240

x*10+55=240

x*10 = 240 - 55

x * 10 = 185

x = 185 : 10

x = 18,5

Answer 3

(x +1) + (x + 2) + ( x + 3) + .....+ ( x + 9) +( x + 10) = 240

10x + (1+2+3+4+...+9+10) = 240

10x + (1+10) + (2+9) +..+(5+6)= 240

10x + 5 * 11 = 240

10x + 55 = 240

10x = 240- 55

10x = 185

x= 185 : 10

x= 18,5

Answer 4

( x + 1 ) + ( x + 2 ) + ( x + 3 ) + .... + ( x + 9 ) + ( x + 10 ) = 240

( 1 + 2 + 3 + ... +10 ) + ( x + x + x + ...+ x ) = 240 

55 + x * 10 = 240

55 + x = 240 :10

55 + x = 24

x = 55 - 24

x = 31 

 Vậy x =31