Question

4+8+12+...396=200 ori x

Answer 1

$4+8+12+...396=200*x \\ 4(1+2+3+..+99)=200*x \\ 1+2+3+...+99=50x \\ \frac{99(99+1)}{2} =50x \\ 99*50=50x \\ x=99$

Answer 2

4+8+12+...+396=200x
4(1+2+3+...+99)=200x
4*(99*100:2)=200x
4(99*50)=200x
4*4950=200x
19800=200x
x=19800:200
x=99