The address of the mathematics department is:

Mathematics and Science Center (MSC), 4th floor
400 Dowman Drive NE, Atlanta, GA, 30322, USA

You may also download a detailed Emory University campus map.

Fly to the Atlanta airport (ATL). It is easiest to take a taxi or shuttle from the airport. In either case, you will go out the doors marked "ground transportation." A taxi stand--marked by a theater rope--will be directly in front of you. Tell the driver to take Briarcliff to North Decatur Road. This will take you to the 5-way intersection ("Emory Village") mentioned below.

If you insist, you can take the subway (MARTA); there is a station (Airport Station) in the airport. Take the Northbound train to Midtown Station, then take the bus (#36 N Decatur Rd/Virginia Highlands in the direction Avondale Station) to the stop Emory Village. The trip will take 45-100 minutes depending on transfer times (e.g. on Sunday the #36 bus only runs every 50 minutes).