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Retirement planning is hard, and most people struggle to understand the fundamentals, according to a new report by the American College of Financial Services, a nonprofit that educates financial advisers. Only 20 percent of people in or near retirement who were surveyed by the group passed a quiz about the basics of retirement planning.

The group quizzed more than 1,000 people ages 60 to 75 who had at least $100,000 in assets. The goal was to gauge how informed people are as they approach retirement, said Dave Littell, a director at the nonprofit. “In some ways, we expected people wouldn’t do that great on the test,” Littell said. “We were surprised at just how bad they did.”

People were most stumped by questions about the strategies that could help their money last longer in retirement. For instance, more people said they would get the biggest boost to retirement income by saving more when they were close to retirement. But pushing back retirement a few years or delaying Social Security would have a bigger impact, Littell said. (Savings set aside at that stage don’t have as much time to benefit from investment growth.)

Gary Koenig, vice president of financial security for the AARP Public Policy Institute, who was not involved in the study, said that people forget that they need to start taking required minimum distributions from their individual retirement accounts and 401(k)s after age 70 1/2.

Others don’t know that taking Social Security benefits at 62 leads to a permanent reduction in benefits, assuming incorrectly that they would start receiving full benefits once they reach full retirement age, he said.

The quiz also highlighted one thing that people often underestimate: how long they will live.