t is amount after time t
Ao is initial amount
t is time
HL is half life
log (At) = log [ Ao x (1/2)^(t/HL) ]
log (At) = log Ao + log (1/2)^(t/HL)
log (At) = log Ao + (t/HL) x log (1/2)
( log At - log Ao) / log (1/2) = t / HL
log (At/Ao) / log (1/2) = t / HL
HL = t / [( log (At / Ao)) / log (1/2) ]
HL = 14.4 s / [ ( log (12.5 / 50) / log (1/2) ]
HL = 14.4 s / 2 = 7.2 seconds
