Question 282915
The key to this problem is setting up the formula. Notice that they have thrown in some extra numbers that are irrelevant just to throw us off.<br>

We take what we know:
<ul> <li> 3% oil mix = 4 gallons
	 <li> 1.5% oil mix = 1/2 gallon.
	 <li> the total quantity is 4 1/2 (4.5) gallons 
	 <li> The question asks for the final percentage oil mix 
</ul>

That is all we need to solve the problem, so let's lay this out in the format 
{{{ pct(qty) + pct(qty) = pct(qty) }}}:
{{{ 3(4) + 1.5(1/2) = x(4.5) }}} <br>
*[invoke explain_simplification "3*(4) + 1.5*(0.5) = x*(4.5)"]<br>
So you can see that the final mixture comes out to  2.8 1/3%  and bob's your uncle!