Final answer:
A higher percentage of daughter isotopes in a rock means that more radioactive decay has occurred and suggests that the rock is older.
Step-by-step explanation:
In radiometric dating, a higher percentage of daughter isotopes in a rock indicates that more radioactive decay has occurred. Daughter isotopes are formed from the decay of parent isotopes, so a higher percentage of daughter isotopes suggests that the rock is older. For example, if the parent-daughter ratio is 1:0.89, it means that 89% of the parent isotopes have decayed into daughter isotopes.