every two days, forty percent of a substance degrades. How many days will it take for 2800 gram sample to decay to below 100 (actively radioactive) grams?

Question

I need help writing an equation for this 

Answer 1

Hi Jenna,

 

If 40% of the substance decays, then the decay factor is 0.60

 

The equation would be.

 

100 < 2800 (.6)^t/2

 

I've listed the exponent as t/2 since the 40% decay occurs every 2 days.