For 25, I would begin with working out the difference in price.
$450 - $360 = $90
Then, $450 is 100% of the cost, therefore we want to know how much it has decreased.
I would work out 1% of $450. [$450 / 100 = $4.50]
Now if we divide $90 (the change in cost) by $4.50, we can tell what percent of a decrease we have.
90 / 4.5 = 20
Therefore we have a 20% decrease.
