1.Betty was showing some snapshots. "Here's one of four generations of my family," she said. "Taken last week at my great-grandmother's 90th birthday party." "That'll be your grandmother," Mary commented, pointing to the photo. "How old is she?" "Figure it out," Betty replied. "Her age, divided by my mother's, gives the same as my great-grandmother's age divided by my grandmother's. And my grandmother was the same age when my mother was born as my mother was when I was born." How old is Betty?

Betty is 17 years old

Betty is 20 years old

Betty is 15 years old