Question

( X + 1 ) + ( X + 4 ) + ( X + 7 ) + .... + ( X + 28 ) = 155

Answer 1

\(\left(x+1\right)+\left(x+4\right)+\left(x+7\right)+...+\left(x+28\right)=155\)

\(\Rightarrow\left(x+x+x+...+x\right)+\left(1+4+7+...+28\right)=155\)

\(\Rightarrow10x+\frac{\left(28+1\right).10}{2}=155\)

\(\Rightarrow10x+145=155\)

\(\Rightarrow10x=155-145\)

\(\Rightarrow10x=10\)

\(\Rightarrow x=1\)

Answer 2

( X + 1 ) + ( X + 4 ) + ( X + 7 ) + .... + ( X + 28 ) = 155

( x + x + ... + x ) + ( 1 + 4 + 7 + 28 ) = 155

28.x + 145 = 155

=> 28.x = 10

=> x = 5/14

Answer 3

(X+1) + (X+4) +(X+7) + ...... +(X+28) =155

= X+(1+4+7+....+28) =155

= X+ (1+4+7+10+13+16+19+22+25+28) =155

=X+145 =155

X=155-145

X=5

Mỗi X bằng : 5 : (28-1):3+1 = 5:10

Mỗi X bằng 0,5