A recent survey of over 1,300 Americans finds that almost 3 out of 4 people aged 60 to 75 failed to pass a quiz measuring financial literacy, and only 5% managed a grade of 80% or better. The poor performance suggests many Americans aren’t making the most of their money in retirement.

Retirement dreams rarely include worrying how to pay bills, yet millions of retirees are doing exactly that. Why? Because Social Security income often falls short, and retirement savings are too small to make up the difference.

According to the Social Security Administration, almost 1 in 4 couples and nearly half of all single retirees count on Social Security for 90% or more of their income. Given the average retired worker collects just $1,360 in Social Security benefits per month, and half of all baby boomers have $50,000 or less in retirement savings, it’s little wonder seniors are struggling to make ends meet.

The American College New York Life Center for Retirement Income asked respondents to answer 38 questions to determine their financial know-how. Though it was a multiple-choice quiz, the questions asked weren’t easy for many to answer correctly.

For example, one question asked if a person with a $100,000 portfolio split equally between stocks and bonds could afford to withdraw 2%, 4%, 6%, or 8% annually and still have a 95% chance of their savings lasting 30 years. Only 38% of people answered correctly that historically, a maximum 4% can be withdrawn per year to achieve that goal.

Another question asked if a 25% drop in account value would have a bigger impact on retirement security if it happened 15 years before retirement, at retirement, or 15 years after retirement. Only 34% of people knew that a drop at the year of retirement puts long-term financial security in retirement most at jeopardy.

The survey results also show that many people don’t know that it’s best to roll traditional IRA assets into a Roth IRA when their tax rate is low, or that a person with a life expectancy of 90 years is generally better off waiting to claim their Social Security at age 70 rather than at their full retirement age.