5:3:2
过D点做BC的平行线,交AF于Q,AE于W,根据相似,因为
WD=BE,所以BM=MD,又BF=4QD,故BN=4ND,即BM+MN=4ND,
即ND+MN+MN=4ND,MN=3/2ND,BM=5/2ND,故答案是5:3:2