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

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:

susie has 7 apples