'Shekels of Silver' in the Bible

My lord, hearken unto me: the land is worth four hundred shekels of silver; what is that betwixt me and thee? bury therefore thy dead.

And Abraham hearkened unto Ephron; and Abraham weighed to Ephron the silver, which he had named in the audience of the sons of Heth, four hundred shekels of silver, current money with the merchant.

Then some Midianite traders passed by, so they pulled him up and lifted Joseph out of the pit, and sold him to the Ishmaelites for twenty shekels of silver. Thus they brought Joseph into Egypt.