A certain element has a half life of 4.5 billion years. (a). You find a rock containing a mixture of the element and lead. You determine that 35% of the original element remains; the other 65% decaye

A certain element has a half life of 4.5 billion years.

(a). You find a rock containing a mixture of the element and lead. You determine that 35% of the original element remains; the other 65% decayed into lead. How old is the rock?

(b). Analysis of another rock shows that it contains 55% of it's original element; the other 45% decayed into lead. How old is the rock.