Husband borrowed Rs.250 from wife

Husband borrowed Rs.250 from wife
After a few days he again borrowed Rs.250
Seeing some money in husband’s bag , she asked husband to return the money*
When asked how much, wife said that he owes her Rs.4100.
On request, below is working given by wife.
1). Rs.       2  5  0
2). Rs.       2  5  0
Total Rs.  4 10  0
Husband is still finding the school where she learned Maths.
Later*
Husband gave her ₹400 back and asked how much balance he has to pay back.
She wrote
₹ 4100 —
₹ 400
————
₹ 100
He gave ₹100 back.
Both lived happily ever after.
Only maths died.