What if the criterion of gold isn’t complete?
Some people have 15,000 or 20,000 rupees. While this amount is equal to the criterion for gold, but this amount does meet the criterion of silver and Zakaat is Compulsory on such people. This ruling is more beneficial to the poor and needy folk and it is Compulsory on such people to give 2.5% of their wealth in Zakaat.
As mentioned in Fath Ul Qadeer, Vol. 2, Pg. No. 227.