回复：回复：回复：让人烦恼的礼金卡问题
justatry
2009-01-06 21:45:31
( reads)
Why not to find r(1-r)/(1-0.9r)'s max?
which would give r = 1 / (1 + sqrt(10%)).
Why not to find r(1-r)/(1-0.9r)'s max?
which would give r = 1 / (1 + sqrt(10%)).