Decimal Reduction Time?

Question

I need help understanding how to figure DRT for microbiology. ex.What is the minimum time that contact lenses with a 10^2 bacteria should be soaked in chlorhexidine .001% that has a DRT value of 383.3 minutes. DRT is the time it takes to kill 90% of bacteria present.I AM NOT GOOD WITH MATH...need simple explanation that I can apply to future problems, PLEASE

Answer 1

based on the info you gave you have 100 bacteria and if you want to kill 90% or the first 90 then the first 383.3 minutes will do that with 10 remaing alive. Now, to kill 90% of them (9 out of the 10 left alive) another 383.3 minutes would have to go by leaving you with 1 last live one which will be dead in the third period of 383.3 minutes for a total of 3 periods of 383.3 min each so 3*383.3= 1149.9 or 1150 min.

Hope this helps. But I think you must be given a formula or some other info.