Question

1×5分之x+5×9分之x+9×13分之x+.+2009×2013分之x=503

Answer 1

1/4*x(1-1/5+1/5-1/9+……+1/2009-1/2013)=503

1/4*x(1-1/2013)=503

503/2013*x=503

x=2013