$4+4-1=7$ 
Ben and Ken have some books. After Ben sends $4$ books to Ken, he has $1$ book less than Ken. Which of the following is true? 

1: Originally, Ben had $3$ books more than Ken. 
2: Originally, Ben had $4$ books more than Ken. 
3: Originally, Ben had $1$ books less than Ken. 
4: Originally, Ben had $9$ books more than Ken. 
5: Originally, Ben had $7$ books more than Ken. 