Answer:

1.      If Randy buys less than five CD’s, Bob’s would be the best buy.  However, at more than 5 CD’s, Joe’s Club is the better buy. If he needed exactly five CD’s, Randy could buy from either Bob’s or Joe’s.  Even though the CD’s are cheaper at Joe’s, Randy would end up paying more for the CD’s because of the membership fee unless he buys more than 5.

2.      I think the table helps Randy the most in making his decision.  I looked at which had the smaller cost for each number of CD’s he might buy.  From 1-4 CD’s, Bob’s costs are smaller.  If Randy is buying 6 or more CD’s, Joe’s costs are lower.  It would cost $75 for 5 CD’s at both stores.  With a table, it’s easier to just look at the numbers.  With graphs, it’s harder to read the exact number.

or

I think the graph helps Randy the most in making his decision.  Bob’s line is lower until 5 CD’s, then they switch and Joe’s line is lower.  The lines meet at 5 CD’s, so at 5 CD’s the prices are the same.  It’s really easy to see with a picture.

or

I think the equation helps Randy the most in making his decision.   If Randy knew exactly how many CD’s he wanted to buy he could just use the equation for each store and find out which would be the better store to buy the CD’s from without making a table or graph.

Teachers Note: 

Any representation would be helpful in making Randy’s decision based on personal preference. 

The differences in the costs are shown numerically in the table. 

The graph shows pictorially the differences in the costs. 

The equation would probably be the least helpful unless Randy knew exactly how many CD’s he wanted to buy.