Explanation

Let's start by using the information that 20% of a is equal to 80% of b. We can write this as an equation:

0.20a = 0.80b

To simplify, divide both sides by 0.20:

a = 4b

Now, we want to find a + b. We can substitute the expression for a in terms of b:

a + b = 4b + b

Combine like terms:

a + b = 5b

Now, we can express this in terms of a by substituting a = 4b:

a + b = 5(1/4)a

a + b = 1.25a

So, the correct answer is: 1.25a