I am looking to do a Ph.D in economics. My GRE quant was 168 so I feel that if I can do well on the rest of my application I can hit a top 15 school.

However, I didn't decide I wanted to do a PhD until it was too late in my undergraduate to get all the math coursework done. Luckily I am close with a few professors in my department, and I will be doing the Masters in economics at my current university starting in the fall. The schedule in that program is loose enough that I will be able to take my remaining math courses during the degree and work on research throughout.

I am graduating with my undergraduate degree this semester and will have completed through Calc III (multivariable calc).

I still need to take: Linear Algebra, Differential Equations, Probability Theory, Real Analysis

Here's the conundrum: I would like to take a math class this summer if possible to alleviate the strain on my coursework during the rest of the year. While none of the above classes are offered, there is a combined "Linear Algebra and Differential Equations" class.

Is it critical that I take full semester versions of both, or would a combined class, combined with a Masters degree, probability theory, and real analysis, still be adequate to build a decent application to a top 15 school?