Question

You are trying to determine the half-life of a new radioactive element you have isolated. You start with 1 gram, and 5 days later you determine that it has decayed down to 0.6 grams. What is its half-life?

Answer 1

Half-life = elapsed time * log(2) / log (bgng amt / ending amt)
half-life = (5 * 0.30103) / log (1/.6)
half-life = (5 * 0.30103) / log (1/.6)
half-life = 1.505 / 0.221848750
half-life = 6.785 days
Location for formulas & calculator
http://www.1728.org/halflife.htm