There are sparrows and pigeons on a fence When five sparrows

There are sparrows and pigeons on a fence. When five sparrows leave, there remain two pigeons for every sparrow. Then twenty-five pigeons leave, and there are now three sparrows for every pigeon. Find the original number of sparrows.

Solution

let x= number of birds on fence
p+s=x
2(s-5)=p
(s-5) =3*(p-25)