(1-1/2^2)(1-1/3^2).(1-1/10^2)
=(2^2-1)(3^2-1).(10^2-1)/(2^2*3^2*.*10^2)
=(1*3)(2*4)(3*5).(8*10)(9*11)/(2*2*3*3*.10*10)
=(1*11)/(2*10)
=11/20