On monday, merlin buys a tablet for $500 from a pads & pods store. on tuesday, he returns to the store and buys a gps device for $200. on wednesday, he downloads $100 worth of tunes from singsong. to be enforceable as a contract, a writing is required for the purchase of

Tablet only.

Explanation:

As Given Merlin have bought tablet for $500, he return it and buy GPS device for $200 and downloaded tunes for $100.

Most of commercial agreement is unwritten and many contract does not require to be in writing, however, uniform commercial code (UCC) have made certain exception for which written contract is required.

Under uniform commercial code (UCC), certain contract for sales of goods Article 2 must be in writing.

All the sales of goods worth $500 and more must have contract in writing and must be signed by the party against which enforcement is sought. It is valid even if the contract is not written in detail, it is enforceable.

Therefore, only purchase of Tablet must have contract in writing as it is worth $500.