Given details are,
Count of bacteria in sample is = 13125000
The increase and decrease of growth rates are = 10%, -8%, 12%
So, let the count of bacteria after 3 hours be = x
By using the formula,
A = P (1 + R/100)
x = 13125000 (1 + 10/100) (1 – 8/100) (1 + 12/100)
x = 13125000 (110/100) (92/100) (112/100)
x = 13125000 (1.1) (0.92) (1.12)
= 14876400
∴ Count of bacteria after three hours will be 14876400.