Answer:
The numbers are;
20 and 21
Step-by-step explanation:
A general form of an exponential decay model can be presented as follows;
f(x) = a·(1 + r)ˣ
Where;
f(x) = The output for a given input variable, 'x'
x = The input variable
a = The initial value
r = The growth (+ve) or decay (-ve) rate
When f(x) = 400, a = 1,800, r = -7% = -0.07, we get;
400 = 1,800 × (1 - 0.07)ˣ
(1 - 0.07)ˣ = 400/1,800 = 2/9
ln((1 - 0.07)ˣ) = ln(2/9)
x = ln(2/9)/(ln(1 - 0.07)) ≈ 20.73
The value of 'x' lies between 20 and 21.
