What is the decay factor in the exponential decay function y=a (1-r) t

Answer:
in this form, the "-r" would cause the result to decrease
I assume that the answer is "r"
if r = .1 (10 %) then 1-.1 = .9
if you have 100 items then y = 100(.9)^1 = 90
the total decreased by 10% ... y = 100(.9)^2 after 2 time periods
Step-by-step explanation: