[Product Question] how can wal mart sell certain products so much less than other places?

Beauty Tips For Body Care
One of the products that I use every day is the Olay regenerist regenerating serum. It often ranges from $20-24 at drugstores and Ulta. I was just browsing wal mart online and saw that it's only $13.19 there. This isn't the first time I've seen a lower price difference for skincare/beauty products at wal mart, but this is the largest price difference I've seen. How can wal mart sell it at almost $10 less? These are the exact same product, am I missing something about how wal mart can sell it for so much less?
Girls Blog 2015
Submitted by basilcilantro