WASHINGTON (AP) — Interest rates on short-term Treasury bills were mixed in Monday's auction, with three-month bills falling to their lowest level in three weeks.

The Treasury Department auctioned $48 billion in three-month bills at a discount rate of 1.740 percent, down from 1.760 percent last week. Another $42 billion in six-month bills was auctioned at a discount rate of 1.905 percent, up from 1.895 percent last week.

The three-month rate was the lowest since March 12, when those bills averaged 1.670 percent. The six-month rate was the highest since the bills averaged 1.950 percent on March 19.

The discount rates reflect that the bills sell for less than face value. For a $10,000 bill, the three-month price was $9,956.02 while a six-month bill sold for $9,903.69. That would equal an annualized rate of 1.772 percent for the three-month bills and 1.950 percent for the six-month bills.

Separately, the Federal Reserve said Monday that the average yield for one-year Treasury bills, a popular index for making changes in adjustable-rate mortgages, stood at 2.09 percent on Thursday, up from 2.06 percent at the beginning of last week on March 26.