To resolve this issue, I did the following: Edit> image size Select "Resample": Preserve Details
change "Resolution:" to 72 for both images ( I used 72, but as long as both images are the same here it should be fine)
hope this can help
...also, under view, I select "print size" to see the actual onscreen size (for this to work, make sure Edit > Preferences > Units & Rulers has the correct Screen Resolution for your screen (PPI based on horizontal pixels, vertical pixels and diagonal size of your screen...lookup Display PPI Calculator to figure it out)