Answer:
74 days
Step-by-step explanation:
The proportion left after d days is ...
p = (1/2)^(d/100)
When that proportion is 60%, we have ...
.60 = .50^(d/100)
log(.60) = (d/100)log(.50) . . . . . take logarithms
100·log(.60)/log(.50) = d ≈ 73.697 ≈ 74 . . . days
