Answer:
There are 2048 megabytes in 2 gigabytes because there are 210 or 1024 megabytes in one gigabyte.
This is complicated slightly by the fact that there are two possible standards. In one (the one used in most computer applications) a gigabyte is 230 bytes and the answer above is correct. In the other (used almost exclusively by drive manufacturers), it's 109 bytes... about 7% less. Under the drive manufacturers' standard, 2 gigabytes is 2000 megabytes (and the megabytes themselves are somewhat smaller as well).