Final answer:
To solve for the number of months it takes for the sweatpants to cost $25, we can use the formula for exponential decay.
Step-by-step explanation:
To solve this problem, we can use the formula for exponential decay:
V = P(1 - r)^t
Where V is the final value, P is the initial value, r is the rate of decay, and t is the time. In this case, we want to find the number of months, so we need to rearrange the formula:
t = log(V/P) / log(1 - r)
Plugging in the values, we get:
t = log(25/1250) / log(1 - 0.21)
Solving this equation gives us t = 13 months.