Aunt Wang's chickens are ducks (3/5), and geese are chickens (7/10). How many known ducks are there, and how many geese are there? (Fill in the number of ducks before answering.)
王大娘养的鸡是鸭的(3/5)，养的鹅是鸡的(7/10)．已知鸭有多少只，求鹅有多少只？(先填写鸭的只数再解答．)
<result>50</result>