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What are the chances a 65-year-old will live past 85? What is the average monthly Social Security benefit? What is the greatest financial risk facing retirees?

Most Americans would flunk a quiz on retirement income issues, according to the MetLife Mature Market Institute, which has updated the Retirement Income IQ Test it first released five years ago. The institute gave an average score of just 43 points out of 100 to more than 1,200 people who took the test in a random survey.

Fewer than one in three people knew how much they could safely withdraw without depleting their savings. Six in 10 underestimated life expectancy and nearly half underestimated the percentage of their pre-retirement income they will need once they retire.

Sandra Timmermann, director of the institute, said she was disappointed scores hadn't improved more in the past five years. "There are still far too many misconceptions about retirement income issues," she said.

Timmermann said the institution's other research indicates a strong interest in continued work, which can significantly boost retirement income.

"Working is the fourth leg of the old three legged stool," of pensions, savings and Social Security, she said. "The more you postpone your annuitization, the larger your payout can be. Work could enable you to generate more income, more assets."

Other findings were:

• Men were much more likely to know the average annual rate of inflation during the past 20 years (3 percent).
• Women were more likely to know the average annual cost of a private room in a nursing home ($78,000).
• Nearly three in four knew at what age a 55-year-old is able to collect full Social Security benefits (66).

The complete version of the study includes the correct answers to the test.

For the record, the chances a 65-year-old living past 85 is 50 percent. The average monthly Social Security benefit in 2007 was $1,078 and the greatest financial risk facing retirees is longevity -- outliving your retirement savings.