PPI as recorded in the jpeg file is irrelevant.   It is common to ask for 72 ppi for displayed images and 240 or 300 ppi for printed images, but these are only conventions, and have no real meaning.  When printing it is possible to tell the printer to use (say) 240 ppi, in which case it will produce a print that measures image-width in pixels divided by 240 inches wide by image-height in pixels divided by 240 high.  It is equally possible to tell the printer to produce a print 12 inches across, in which case the resolution will almost never be 240.