Please help, need answer asap (drake question)

My brother was going to pick up 4 eggs for my incubator and bring them to me Friday (welsh harlequin) ...he's coming from 4 hours away. The sellers other runner duck just got into the pen with his welsh harlequin duck this morning so he now has only one purebred egg for me (collected yest). The eggs being laid tomorrow, Thursday and Friday may be mixed. What are the odds the other 3 eggs will be mixed breed with his runner drake? I'd appreciate an answer or idea so I can decide to get them or not. Thank you!!!