Praise be to Allah.
What must be given as zakah on cash is one quarter of one tenth (2.5%), or 25 out of every thousand.
The way to work out the zakah on cash is to give 25 riyals for every thousand. So if you have ten thousand, the zakah is 250 riyals.
You can divide the amount (that has reached the nisab or minimum threshold at which zakah becomes due) by forty, and whatever results from that division is the amount of zakah that must be paid.
Based on that, if you divide 10,000 riyals by 40, the result will be 250 riyals. This is the amount of zakah for that amount [of cash].
For more information, please see the answer to question no. 2795 .
And Allah knows best.