Question

tìm x biết ( x + 5 ) + ( x + 10 ) + ................ ( x + 60 ) = 474

Answer 1

\(\left(x+5\right)+\left(x+10\right)+...+\left(x+60\right)=474\\ \Rightarrow\left(x+x+...+x\right)+\left(5+10+...+60\right)=474\\ \Rightarrow12x+390=474\\ \Rightarrow12x=84\\ \Rightarrow x=7\)

Answer 2

\(\left(x+5\right)+\left(x+10\right)+...+\left(x+60\right)=474\\ \left(x+x+...+x\right)+\left(\dfrac{\left(60+5\right)\left[\left(60-5\right):5+1\right]}{2}\right)=474\\ 12x+390=474\\ 12x=474-390\\ 12x=84\\ x=84:12\\ x=7\)