Q: How can you tell what the large date and the small date on the 1982 pennies are? What the 4 different 1982 pennies?

A: The large and small date are pretty easy to tell when you have them both together. The other variations are based on the metal content. For a more detailed description, here is a quote from a site discussing that very issue:

Partway through production of 1982 Lincoln cents, the U.S. Mint changed the coins' composition from brass (95 percent copper and 5 percent zinc) to one that is predominantly zinc (a core of 99.2 percent zinc and 0.8 percent copper with a copper barrel plating). Cents dated 1982 come in both metallic varieties - and to complicate matters even more, there are large-date and small-date versions in both compositions. Viewed side by side, the large and small dates are relatively easy to tell apart, and there isn't much money riding on the difference, since both are quite common. Distinguishing between the brass and zinc cents is easiest by weight, rather than color: The brass cent is heavier, at 3.11 grams versus 2.5 grams for the zinc cent. Again, both kinds are common. In all, there are seven different varieties of 1982 cents. Just one combination is missing: There is no small-date cent in brass from the Denver Mint.

(via pcgs)