Step-by-step explanation:

Let the original number be x

It is increased by r%,so our new number is (100+r)% of x

=x*(100+r)/100

To get back to the original number,let’s say it is reduced by y%,

So, we basically have to find the value of y in terms of r.

[x*(100+r)/100]*(100-y)/100=x

x(100+r)(100-y)/10000=x

Cancelling x from both sides,we get

(100+r)(100-y)=10000

100-y=10000/(100+r)

y=100-[10000/(100+r)]

=(10000+100r-10000)/(100+r)

=100r/(100+r)