The paint mixer should mix 1.25 gallons of 30% gloss paint with 2.5 gallons of 15% gloss paint. Hence, option B, 1 1/4 is correct option.
To solve this problem, we can use a system of linear equations. Let's denote:
-
as the amount of 30% gloss paint in gallons.
-
as the amount of 15% gloss paint in gallons.
We have two conditions to satisfy:
1. The total volume of the mixture should be 3.75 gallons.
2. The final mixture should have a gloss percentage of 20%.
The first condition gives us the equation:

The second condition involves calculating the total amount of gloss in the mixture. The amount of gloss in the 30% gloss paint is
(since it's 30% of
), and the amount of gloss in the 15% gloss paint is
. The total amount of gloss in the final mixture should be 20% of 3.75 gallons, which is
. This gives us the equation:

Now, let's solve this system of equations:
1.

2.

First, we'll simplify the second equation:

Now, we have:
1.

2.

We can solve this system using various methods, such as substitution or elimination. Let's use the substitution method. From the first equation, we can express
in terms of
:

Substitute this into the second equation:


Solving for
:

Now substitute
back into
to find
:

So, the paint mixer should mix 1.25 gallons of 30% gloss paint with 2.5 gallons of 15% gloss paint. Hence, option B, 1 1/4 is correct option.