Today's cosmic question:   What's the best investment a retired person can make these days?

Answer: Getting a day job.

I'm serious. Investment returns are so low millions of retirees need to think about going back to work, at least part time.

You can understand why by doing an exercise with me. First, we're going to figure out how much money you can make working an 8 hour day, one day a week, 52 weeks a year. Then we're going to see how much you'd need to invest to produce the same amount of cash income.

Gird yourself.

The largest employer in the United States is Wal-Mart. With 1.3 million "associates" the company employs three times as many people as General Motors (386,000).   Indeed, Wal-Mart employs more than the next three largest employers--- General Motors, McDonalds (364,000), and United Parcel Service (359,000)--- combined. It also employs twice as many people as IBM (316,000) and GE (313,000) combined.

We're talking big. Very, very big.

That makes Wal-Mart a prime source of jobs. To paraphrase bank robber Willie Sutton, we'll look there "Because that's where the jobs are." It also helps that Wal-Mart is growing while most of corporate America is shrinking.

Sorry, you probably won't get a job as a Wal-Mart Greeter. As gigantic as the company is, there are only 1,568 Wal-Mart stores, 1,258 Wal-Mart Supercenters, and 525 Sam's Clubs in the United States. That's a total of 3,351 stores. So if you're going to work at Wal-Mart you shouldn't count on being a greeter--- even though the company plans to add nearly 300 stores in the coming year.

Although the starting wage is definitely lower, a recent analysis indicates that most Wal-Mart employees work less than 30 hours a week, don't have health insurance, and earn $8 to $9 an hour.

So if you worked one eight-hour shift at Wal-Mart every week and earned $8.00 an hour, you'd gross $3,328 for the year before employment taxes of 7.65 percent. That means your after-employment tax wages would be $3,073.   (Sorry to seem so persnickety about this but your don't have to pay employment taxes on your interest and dividend income and we want an apples to apples comparison.)

Now comes the hard part. We take the family checkbook to the different investments and write a check large enough to earn $3,073 in a year.

First we'll try something easy, buying a one-year Certificate of Deposit. According to Banxquote, the national average yield on a 1-year CD was 1.11 percent. That means you'll need to buy a CD in the amount of $276,883. That's a rather hefty sum.

All right, then.

Let's try a 2-year Treasury note. According to Bloomberg those are currently yielding about 1.53 percent. To equal working at Wal-Mart you'll need to commit $200,876 to the U.S. Treasury.

Let's try stocks.

If we invest in a major index fund, like Vanguard 500 Index, we'll earn 1.72 percent in dividends. We'll have to write a check for $178,686 to equal our income from Wal-Mart. (Wal-Mart stock itself, by the way, yields only 0.6%   so you'd need to invest $512,235 to produce the income of a single shift.)

How about a longer commitment? Right now, yields on 5-year bank CDs are 2.97 percent, slightly better than the 2.75 percent yield on 5-year Treasury notes. We'll only need $103,482 in a 5-year CD to produce $3,073.

Finally, we can make a long-term commitment and put our money in a 10-year Treasury. They're currently yielding about 3.79 percent. So if you have $81,092, you'll be able to equal the income you can earn by working one day a week at Wal-Mart.

Unfortunately, we have a problem.

According to the most recent Federal Reserve report on Consumer Finances, half of all American households have a net worth of $80,700 or less.

Websites:

Bank CD rates

Treasury yields

Wal-Mart website

Hostile site Wal-Mart store locator

Wal-Mart Class Action Suit information