Duration adjustment using Swaps / Questions from the CFA online Qbank

Can someone explain the solution?

Question:

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.

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

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.

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=20,000,000×3−5−3.62511,030,000=20,000,000×3−5−3.625

C is incorrect because 9,412,000=20,000,000×2−3−2.1259,412,000=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=20,000,000×2−5−3.37517,777,000=20,000,000×2−5−3.375

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

Using the formula target duration should be always 3? and bond portfolio duration is always 5? only swap duration should differ between the calculation but I don’t understand their explaination

why are they using different numbers in explaining why it isn’t answer B and C

Please clarify someone, thanks in advance!

??? someone?

Different numbers in B and C because those are different swaps with differing maturity.