Question

a number is increased by 20% and then decrease by 20% find the net increase or decrease percentage

Answer 1

Let the number be y
increase of 20%=y+y×20%
=y+y×20/100
=y+y/5
=5y+y/5=6y/5
Then decrease of 20%=6y/5-6y/5×20%
=6y/5-6y/5×1/5
=6y/5-6y/25
=6y×5-6y/25
=30y-6y/25
24y/25
Net increase or decrease =y-24y/25
=25y-24y/25
y/25
Therefore it decreases by y/25
And it's percentage=y/25 ×100=4y= 4%
So it decreases by 4%

Answer 2

Let the number be 100
after increasing of 20% the number be =100+100×(20/100)=120
and again decreasing of 20%the number be =120-120×(20/100)=96
So the new number be 96 and original be 100 then total decrease of 4 by 100=(4/100)×100=4%.. Answer