Suppose the value of a house has changed from $64 000 to
$80 000, then it has increased in value by $16 000. so its
fraction change is 16000/ 64000 = 1/4. And its percentage
change is 1/4 x 100% = 25%.

When a percentage change is given, for e.g. in a sale at
a sports shop all the goods may be advertised as 15% off marked
prices, then the reduction in price of a tennis racket marked
as £80 can be found by finding 15% of $80 as mentioned
below:

15/100 x $80 = $12.