suatu unsur radioaktif meluruh dan tinggal 25℅ dari jumlah semula setelah 10 menit. bila mula mula massa unsur tersebut 100gr, maka setelah setengah jam meluruh

Nt = No. (1/2)^t/T
25% No = No . (1/2)^t/T
1/4 = (1/2)^t/T
(1/2)^2 = (1/2)t/T
2 = t/T
2 = 10/T
T = 5 menit (waktu paruh)

Nt = No (1/2)^t/T
Nt = 100 (1/2)^30/5
Nt = 100 (1/2)^6
Nt = 100 . (1/64)
Nt = 1,56 gram

Peluluhan.
Kelas XII kurikulum 2013 revisi 2016.

N = N₀ (1/2)^(t / T_1/2)
25% N₀= N₀ (1/2)^(10 menit / T_1/2)
1/4 N₀ = N₀ (1/2)^(10 menit / T_1/2)
(1/2)² = (1/2)^(10 menit / T_1/2)
T_1/2 = 300 s

N = N₀ (1/2)^(t / T_1/2)
    = (100 g) (1/2)^[10 menit / (5 menit)]
    = 25 g