I would like to use two different fonts in my document, differentiated as follows: In the body/text of my document, I would like to use Times, and in the equations I would like to default to standard computer modern. Additionally, if any text should appear in my math environments, I would like that to be rendered in Times as well. How can this be done?
To change just the text-mode font to Times, while leaving the math-mode font family at its default (i.e., Computer Modern), you could issue the command
in your document's preamble.
As the name of the command suggests, this instruction only changes the font for the "roman" text font. As such, the default sans-serif and monospaced font families are also left untouched. If you also wanted to change the sans-serif font family from Computer Modern to, say,
Helvetica, you could add the command
where the 0.86 scaling factor is chosen to equalize the "x-heights" of Times Roman and Helvetica. At a given "point size", the x-height of Helvetica is about 20 percent larger than that of Times Roman; if there's a chance that both fonts will occur side by side in a line of text, it's imperative to scale one font or the other so that the x-heights are (roughly) equal.
For the sake of completeness: assuming you have an up-to-date TeX distribution (such as TeXLive2012, or MikTeX2.9 with all packages fully updated) on your computer, you could also issue the command
to switch the document's text-mode font to Times Roman. Any differences between the Times Roman text families of the
newtxtext groups will be very subtle.