Q. I have a grandson who is 38 years old. He is a responsible young man, regularly employed. But his earning power is limited, probably between $25,000 and $35,000 a year (in today’s dollars) in his lifetime. When my wife and I die (we are 87 and 90 years old) he will inherit about $500,000.

Can you recommend an allocation in a "couch potato" type portfolio that has a low management fee? He is completely unsophisticated about stocks, bonds, annuities, or any other type of investments. He thinks he can invest by talking to his friends, or that he can search the yellow pages to find an "investment advisor" whose primary goal would be to make money for the investor. —J.N., San Antonio, Texas

A. There are two possible solutions here. The first is simple: Buy shares in a single mutual fund that will be invested in a broad portfolio. One example is Vanguard Wellington Admiral shares (ticker: VWENX), which I have mentioned frequently. This is a balanced fund that can be purchased without commission. It also has a very low expense ratio.

Recently, the fund had an annual yield of 3.06 percent. The fund has done better than 94 percent of its competing peers over the last 15 years, according to Morningstar. Over the last three dismal years the fund gained 0.63 percent a year. The average moderate risk allocation fund lost 1.49 percent a year.

Your son can invest in this fund and be sublimely indifferent to the markets, provided only that he not spend any more than the fund generates in dividend and interest income. He can arrange for this to be sent to him automatically.

Choices in this area are expanding rapidly. New portfolios of broadly diversified index funds are being introduced regularly.

Unfortunately, lots of people will be interested in selling him financial products. They will be interested from the day he inherits. The most passionate people will be hawking the high-commission “solution” that works best for them.

The second solution is to find a registered investment advisor. This is a person who manages assets for people and is sworn to act as a fiduciary— putting the client’s best interest first. I suggest that you do this now, while you are still living, rather than leaving it up to your grandson. Take your time, visit several, and don’t be impressed by fancy offices. The service will likely cost you about 1 percent a year, plus the cost of the underlying investments.

This is a material cost, but it should be viewed as a defense against the unrelenting marketing of far more expensive investment products. Most $500,000 accounts are invested in mutual funds, not individual securities. Just make sure the advisor focuses on low-cost index mutual funds or low cost exchange traded funds (ETFs).

Having the management of your/his financial assets in place today will avoid a hasty scramble later. It would probably be a good thing for you, too, since many people are incapacitated long before they die.

Q. I have a dear friend of the family who turned 90 this year. She has worked hard and saved all her life. Her grandson will inherit her savings. He is 30 years old. What would you recommend a young person to do with such an inheritance? He has a good job and saves too. —T.W., by email

A. What he does depends very much on the size of the inheritance. It could be used, for instance, as a substitute for retirement savings if it is large enough. Suppose, for instance, that the inheritance is equal to 2 years of his current income. If it grows at an after-tax rate of 6 percent a year, it would double every 12 years, so it will have multiplied to 16 years of his current income by age 66. That’s more than he would accumulate in a qualified plan.

Another viewpoint is for him to invest the money in a low-cost diversified fund, spend the income only, and reinvest all capital gains. This will be a nice supplement to his earned income. The larger the inheritance, the nicer the supplement.

Either way, the best investment would be a well-diversified, low-cost portfolio. One option is to build one of my Couch Potato Building Block portfolios. Trailing performance data on these low-cost, self-managed portfolios is updated monthly on my website, www.assetbuilder.com. Another solution is to buy a single mutual fund that offers a broadly diversified portfolio at low-cost.