[" 3) "8000" years "],[" 15.After a certain lapse of time,the fraction "],[" radioactive polonium undecayed is found to "],[12,5%" of initial nuantity.The duration of th "],[" time lapse is (if the half-life of polonium is "1" ? "],[" days) "],[" 1) "414" days "2" ) "407" days "3" ) "421" days "4" ) "410" day? "]