LA Johnson/NPR

Summertime means summer jobs for many college students. But a summer job just doesn't have the purchasing power it used to,

especially when you compare it with the cost of college.

Let's take the example of a working-class student at a four-year public university who's getting no help from Mom and Dad.

In 1981-82, the average full cost to attendwas $ 2,870. That's for tuition, fees and room and board.

The maximum Pell Grant award back then for free tuition help from the government was $ 1,800. That leaves our hypothetical

student on the hook for just about $ 1,000. Add in a little pocket money, too — say $ 35 a week. That makes an extra $ 1,820

for the year on top of the $ 1,000 tuition shortfall.

Now, $ 3.35 an hour was the minimum wage back then. So, to make $ 2,820 meant working 842 hours. That's 16 hours a week year-round

— a decent part-time job. It's also about nine hours a day for three straight months — a full-time, seven-day-a-week summer job.

Or, more likely, a combination of both. In short: not impossible. Far from it.

For today's public university student, the numbers have all changed in the wrong direction.

Here's what we calculated based on last year's numbers.

"The minimum wage has also gone up more slowly than the cost of college. It's $ 7.25 an hour. At that rate, a student would have to work 1,771 hours to get by. That's 34 hours a week, every week of the year. To cover today's costs with just a summer job, a student would have to lose a little sleep, working almost 20 hours a day for three straight months. And that would still leave no money for books, travel home, pizza or a trip to the movies."

This year, based on the new full cost of attendance, things are even worse.

In 2014-2015, the school year just ended, the total of tuition, fees and room and board for in-state students at four-year public

universities was $ 18,943. The maximum Pell Grant didn't keep pace with that: It was $ 5,730. That left our hypothetical student

on the hook for $ 13,313.

A student would now have to work 35 hours a week, every week of the year, to get by. To cover today's costs with a low-skilled,

minimum wage summer job? Over 90 days, a student would need to work 20.24 hours a day.

Plus side: if you're working that much, you don't need to pay rent because you're hardly sleeping.

There's also this: Research shows that when college students work more than 20 hours a week their studies suffer. If they're

working full time, many will take longer to finish ... and end up paying even more.

No wonder students are borrowing so much these days.

A version of this story was published on NPR Ed in June 2014.