posted by fred .
pierre was born in the twentieth century and will be x years old in the year x squared. In what year was pierre born
Let y be the year of his birth. x^2 is the year when he is x years old.
x^2 - y = x
x^2 -x = y must be between 1900 and 2000
Try x = 45. His birth year would be 1980
If x = 46, his birth year would be 2070 (too late)
If x = 44, his birth year would be 1892 (too early).
So the birth year is 1980