"If somebody says they want to come build something here, are they hiring African workers?" Obama said. "If somebody says that they want to help you develop your natural resources, how much of the money is staying in Africa? If they say that they're very interested in a certain industry, is the manufacturing and value-added done in Africa? "
Obama did not specifically mention China, but some African leaders have criticized Beijing for such behaviors.
Obama's focus on trade and business appeared to be well received in Africa, home to six of the world's 10 fastest-growing economies. The majority of the questions he received from the South African press and later at a town hall meeting with young African leaders focused on U.S. economic interests in the region.
Between his two events, Obama spent 30 minutes meeting privately with two of Mandela's daughters and several of his grandchildren at the former leader's foundation offices in Johannesburg. He also spoke by phone with Mandela's wife, Graça Machel, who remained by her husband's side at the Pretoria hospital where he has battled a lung infection for three weeks.
In a statement following the call, Machel said she drew strength from the Obama and his "touch of personal warmth."
Obama, who has met Mandela in person only once before, did not visit the former leader in the hospital out of respect for his family's wishes, the White House said. Ahead of his arrival in South Africa, the president had told reporters that he did not need "a photo-op" and didn't want to be obtrusive.
Obama ascent to the White House has drawn inevitable comparisons to Mandela. Both are their nations' first black presidents, symbols of racial barrier breaking and winners of the Nobel Peace Prize.