It will take a boatload of time to resize that boatload of scanned images one at a time.
To resize them more quickly, process all of them at one time as a batch using the freeware program, IrfanView.
Get the small installation file from www.irfanview.com and install the program.
Start the program and then choose from the menu bar: Edit > Batch conversion
A dialog box (window) labeled "Batch convesion" pops up.
1) Verify the file output format (JPG).
2) Check the box for "Use advanced options" (left hand side underneath "Output format"). "Advanced" button no longer grayed out.
3) Click the "Advanced" button.
New dialog box opens up (pop-up window). Pop-up window is labeled as "Settings for all images:"
4) Click "Resize".
5) Make the changes to the size you'd like. (Percentage of old file, new file dimensions, etc.)
6) Make sure "Preserve aspect ratio" is checked!
7) Click "OK".
"Settings for all images" window closes.
Back at "Batch conversion" window.
On right side of window, navigate to the folder where the pictures you want to resize are located.
8) Click on the picture files and then click "Add" to add the image files to the list to convert. (Or click "Add all" to resize all of the images in that folder.)
9) Batch conversion will place the processed image files into the "C:\Temp" folder by default. If you don't want it to do that, then you will need to point the "Outout directory for result files:" option to the desired folder.
10) Click the "Start Batch" button to start the conversion process. (Bottom left corner.)
Sit back.