Q. I'm on Medicare and have a company insurance policy that is part of my retirement package. I also purchased another health insurance policy in case my former employer were to take away the insurance it currently provides. While I have both policies, will they both pay for expenses?

A. The two private policies will not pay for the same expenses. They will seek "coordination of benefits" to make sure that only one of them pays for the expenses that Medicare does not cover. This is why it is not useful for most individuals to have two policies to supplement Medicare. If you fear loss of insurance from your former employer, however, purchasing such coverage now does guarantee that you will have coverage in the future. The rules governing Medicare private supplemental policies ensure that everyone can purchase it when they turn age 65, but after a six-month period in which enrollment is guaranteed, private plans do not have to sell you a policy.

Q. My mother is in a nursing home, which is being paid for by Medicaid. The Medicaid officials said she can keep $40 a month out of her Social Security. How do they come up with the $40?

A. Medicaid requires that individuals pay most of their income to defray the costs of a nursing home stay before Medicaid payments begin to fill in the gap. The $40 a month amount is what she is allowed to keep of her income for incidental expenses.

Q. My husband is a federal retiree. He has Medicare A and B and federally sponsored standard option retirement coverage. Do we also need a Medigap policy?

A. A Medigap (private supplemental) policy would be redundant for you. The combination of Medicare and federally sponsored retirement coverage will provide you with very comprehensive insurance. Medigap plans are designed to fill in gaps left by Medicare, and since such gaps will be paid by your federal insurance policy, the Medigap plan will not provide duplicate payment. For most people, it makes no sense to have more than one supplemental policy if they have Medicare. And your federal coverage is a better deal than buying Medigap.

Do you have questions about health care coverage? Changes are occurring in the medical marketplace, and the debate over costs, quality and access to care continues. The Washington Post free telephone information service can take your questions. Call POSTHASTE at 202-334-9000 on a touch-tone phone and enter category code 8500 (in Prince William County, 703-690-4110). Economist Marilyn Moon of the Urban Institute provides answers in a periodic column.