Given that a is the average (arithmetic mean) of the first five positive multiples of six and b is the median of the first twelve positive multiples of six, what is the ratio of a to b?  Select
A) 3:4  B) 6:13  C) 5:6  D) 13:10  E) 4:3
The first nine positive multiples of six are {6, 12, 18, 24,30}   The first twelve positive multiples of six are {6, 12, 18, 24, 30,36,42, 48, 54, 60, 66, 72}   Both sets are evenly spaced, thus their median=mean:   a=18 and b=(36+42)/2= 
<gadget id="calculator">(36+42)/2</gadget>
<output>39</output>
39 --&gt; a/b=18/39=6/13.   Answer: 6:13.
<result>B</result>
Given that a is the average (arithmetic mean) of the first five positive multiples of six and b is the median of the first twelve positive multiples of six, what is the ratio of a to b?