# A bacteria culture doubles every 0.25 hours. At time 1.25 hours, there are 40 000 bacteria present. How many bacteria were present initially?

They double every 0.25 hours, so at 1.25 hours, they have doubled $\frac{1.25}{0.25} = 5$
So this makes ${2}^{5}$. ("Double" would mean use Base 2)
$\frac{40 000}{2} ^ 5 = 1250$