Hello, me and my teacher are having a debate regarding the average percentage of change between 2 sets, 2 numbers in each set. The sets are trials for a science experiment, the numbers for each set are before and after. So set A would be A1 for before experiment and A2 for after. I calculated the percentage change for both sets individually and divided it by 2 to get my average, my teacher, however, averaged the start experiment digits (A1 + B1) and the post-experiment digits (A2+B2). He then plugged the average numbers into the percentage change formula, we got different answers, here is the raw math:

My way:
A = (11.8 – 9.8) / 9.8 x100 = 20.4082% increase

B = (12.5 – 10.9) / 10.9 x 100 = 14.6789% increase

A+B = 35.0871

35.0871 / 2 = 17.54355



Teacher way:
(A1 + B1) / 2 = 10.35

(A2 + B2) / 2 = 12.15

(V2-V1) / V1 x 100 = (12.15 – 10.35) / 10.35 x 100 = 17.3913…%

The answer have a decimal difference any my question is regarding which one is more accurate for the experiment at hand.

-Thank you