September 15th, 2005, 4:06 pm
Think about it this way. If interest rates go up one basis point, the original bond will decline in price by four basis points or $8,000. Floater A will decline in price by 1 basis point or $1,600. Floater B will decline in price by 0.5 basis points or $100. So the inverse floater must decline in price by $8,000 - $1,600 - $100 or $6,300.The market value of the inverse floater is $20 million - $16 million - $2 million = $2 million. $6,300 / $2,000,000 = 0.00315 = 31.5 basis points. So the duration of the inverse floater must be 31.5.