Answer:
4.048 hours
Step-by-step explanation:
A = Pe^(rt)
After 1 hour, the amount decreases by 29% (A = 0.71P), so r is:
0.71P = Pe^(r×1)
0.71 = e^r
r = ln(0.71)
r = -0.342
P = 400. When A = 100, the time t is:
100 = 400e^(-0.342 t)
0.25 = e^(-0.342 t)
ln(0.25) = -0.342 t
t = -ln(0.25) / 0.342
t ≈ 4.048
Approximately 4.048 hours have passed.
