Question

a number is increased by 10% and then decreased by 10% find the net increase or decrease percent

Answer 1

let the number be 100
if it is increased by 10%
resulting no = 110
if the no is decreased by 10%
resulting no is 99
so the net result is decrease of 1%

Answer 2

Dear Ththteh,
Assume the  number to be 100 for instance, 
10% of 100 increased = 100 + ( 10/100*100 )
= 100 + 10 = 110
The resulting number decreased by its 10% = 110- (10/100*110)
= 110-11 = 99
Now, net decrease =100-99 = 1
Decrease percent = (Decrease / Original number * 100) %
= ( 1 / 100 *100 )% 
= 1%.
Hope this helps...