Li Ching-Yuen himself gave a hint as to the secret of long life. It was

* Keep a quiet heart * Sit like a tortoise * Walk sprightly like a pigeon * Sleep like a dog

If this hint is not enough to help, try plotting the data on a chart. If there is a 50% chance, say, of death each year, by what factor might the expected numbers of living very old people reduce over 5 years? Can you find a percentage which might fit the data?