2x/(1*3)+2x/(3*5)+2x/(5*7)+2x/(7*9)+2x/(9*11)=10
2x*1/2(1-1/3+1/3-1/5+1/5-1/7+1/7-1/9+1/9-1/11)=10
x*(1-1/11)=10
10/11x=10
x=11