30. (a) Replacing differentials with deltas in Eq. 43-11, we use the fact that "N = -12 during "t =1.0 s to obtain "N = -"t =Ò! =4.8 × 10-18/s N where N =2.5 × 1018, mentioned at the second paragraph of ż43-3, is used. (b) Eq. 43-17 yields T1/2 =ln 2/ =1.4 × 1017 s, or about 4.6 billion years.