Rates mixed in Treasury bill auction

The Treasury Department auctioned $15 billion in three-month bills at a discount rate of 4.775%, up from 4.73% last week. An additional $13 billion in six-month bills was auctioned at a discount rate of 4.81%, up from 4.735% last week.

The new rates understate the actual return to investors -- 4.914% for three-month bills, with a $10,000 bill selling for $9,879.30, and 5.013% for a six-month bill selling for $9,755.49.

Separately, the Federal Reserve said the average yield for one-year Treasury bills, a popular index for making changes in adjustable-rate mortgages, fell to 4.86% last week from 4.89% the previous week.