Resize Image Mac Air. Choose view show view options then make your changes. Once all images are selected go to tools adjust size.
All the images will open in preview. Once all images are selected go to tools adjust size. Choose percent from the pop up menu next to the width and height fields then enter the percentage in those fields.
After that go ahead and right click on all on the image that you have chosen and launched it on preview.
If you want to crop out a part of the image to resize see cropping an image in preview. Choose view show view options then make your changes. Select tools adjust size to bring up the resize dialog which will allow you to resize the image. It supports many measurement units including pixels.