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Julia: How Does Her Fifth Kilometer Time Compare to Her First?

GMAT-JCBRLF

Julia is a professional runner. Her top speed is running a kilometer in $3$ minutes, but for each kilometer after that, she gets $10\%$ slower. Assume that in any race her first kilometer is run at her top speed.

If Julia is running 5K next weekend, approximately how much longer does the last kilometer take than the first kilometer?

A

$60$ seconds

B

$72$ seconds

C

$84$ seconds

D

$87$ seconds

E

$90$ seconds