MATH PUZZLE: Can you replace...

A minister decided to do something a little different one Sunday morning. He said, "Today, in church, I am going to say a single word and you are going to help me preach. Whatever single word I say, I want you to sing whatever hymn comes to your mind."The pastor shouted out, "Cross!" Immediately the congregation started singing, in unison, "The Old Rugged Cross." The pastor hollered out, "Grace!" The congregation began to sing "Amazing Grace, how sweet the sound..." The pastor said, "Power." The congregation sang "There Is Power in the Blood." The Pastor said, "Sex." The congregation fell in total silence. Everyone was in shock. They all nervously began to look around at each other, afraid to say anything. Then all of a sudden, way from in the back of the church, a little old 87-year-old grandmother stood up and began to sing "Precious Memories."