In Kaplan Schweser 2019, page 103 of Fixed Income, 4th Q says 
The current price of a $1,000, 7 year, 5.5% semi annual coupon bond is $1,029.23. The bond’s price value of a basis point is closest to 
a) $0.05



In the answer, They have subracted 1,029.23 by the price of +0.01% . 
Why have the not taken the average of the price of +0.01% and -0.01% ??