=1/4*(1-1/5)+1/4*(1/5-1/9)+1/4*(1/9-1/13)+……+1/4*(1/37-1/41)
=1/4*(1-1/5+1/5-1/9+1/9-1/13+……+1/37-1/41)
=1/4*(1-1/41)
=10/41