So for this, you'll be using an exponential equation, which is y=ab^x (a = initial value, b = growth/decay).
Since you start off paying your friend $1, that will be your initial value. And since this is a 50% increase, you are to add 1 and 0.5 together (50% in decimal form), which is 1.5. That will be your b variable. And since # of days is the independent variable, that will be your x variable.
Using the previous info, this is our equation: y = 1(1.5)^20 . From here we can solve for the total cost (y).
Firstly, solve 1.5^20: y = 1(3325.26)
Next, multiply everything on the right side of the equation, and your answer will be (rounded to the hundreths): y = 3325.26
In context, at the end of the 20 days, you have to pay your friend $3325.26.
