Stumped by a CFAI practice question

As I’m doing my final prep before tomorrow I am taking a few more CFAI practice item sets. In derivatives, the following question came up and I completely unable to think of why a swap of 3.5 years is used. Maybe someone here can help me out? Shouldn’t the two year swap be used since they want to reduce duration by 2 years?

Q. Based on the data in Exhibit 2, modifying the duration of the fixed-income allocation to its target will require an interest rate swap that has notional principal closest to:

  1. $11,030,000.
  2. $17,777,000.
  3. 9,412,000. **Investment**** Amount **** ( millions) **Risk Measure A-rated corporate bonds 20 Duration: 5.0

Lehigh intends to synthetically modify the duration of the corporate bond component of the portfolio to a target of 3.0 in anticipation of rising interest rates. Interest rate swap data are provided in Exhibit 2.

EXHIBIT 2

PAY-FIXED INTEREST RATE SWAPS

Swap** Maturity **Duration A 2 years −2.125 B 3 years −3.375 C 3.5 years −3.625

Solution

A is correct.

NP=B×(MDURT−MDURB)MDURSNP=B×(MDURT−MDURB)MDURS

where

NP = notional principal

B = bond portfolio

MDUR_T_ = duration target of portfolio

MDUR_B_ = duration of bond portfolio

MDUR_S_ = duration of swap

11,030,000=20,000,000×3−5/3.625

C is incorrect because 9,412,000=20,000,000×2−3/2.125

In the numerator, 2 represents the target reduction in duration, and 3 represents the new target duration.

B is incorrect because 17,777,000=20,000,000×2−5/3.375

In the numerator, 2 represents the target reduction in duration, and 5 represents the current duration.

I’m guessing you don’t care about the answer to this now :slight_smile:

But in case anyone else finds it useful. Always use the swap with the higher duration. As it results in smaller notional principal of the swap. That’s the preferred approach in CFA.