(1+1/2)(1+1/4)(1+1/6)……(1+1/10)(1-1/3)(1-1/5)……(1-1/9)
=3/2*5/4*……*11/10*2/3*4/5*8/9
=(3/2*2/3)*(5/4*4/5)*……*(9/8*8/9)*11/10
=11/10