(1+1/1*3)*(1+1/2*4)*(1+1/3*5)*(1+1/4*6)*...*(1+1/9*11)
=(1+1*3)*(1+2*4)*(1+3*5)*(1+4*6)*...*(1+9*11)/(1*2*3²*4²*...9²*10*11)
=(2²*3²*4²*5²*...*9²*10²)/(1*2*3²*4²*...9²*10*11)
=2*10/11
=20/11
(1+1/1*3)*(1+1/2*4)*(1+1/3*5)*(1+1/4*6)*...*(1+1/9*11)
=(1+1*3)*(1+2*4)*(1+3*5)*(1+4*6)*...*(1+9*11)/(1*2*3²*4²*...9²*10*11)
=(2²*3²*4²*5²*...*9²*10²)/(1*2*3²*4²*...9²*10*11)
=2*10/11
=20/11