The price of a notebook was

$3.90

yesterday. today, the price fell to
$3.40
. find the percentage decrease. round your answer to the nearest tenth of a percent.

Old price: p1 = $ 3.90;

New price: p2 = $ 3.40.

The percentual decrease is given by

d(%) = [ (p2 - p1) / p1 ] * 100 %

d(%) = [ (3.40 - 3.90) / 3.90 ] * 100 %

d(%) = [ - 0.50 / 3.90 ] * 100 %

d(%) = - 0.128 * 100 %

d(%) = - 12.8 % (approximately)

So the price fell 12.8 % approximately.

I hope this helps. =)

Answer is a not really sure tho