A girl bought a box when she was 20, She puts $250 in the box on every birthday And her sister takes out $50 from the box on her birthday. Girl died when she was 60 and when the box was opened there were $500 remaining in the box.
How is it possible?
See Answer:Girl and the box
In 40 years she put 10(as her birthday comes once in 4 years)*250 = $2500
Her sister withdraws 40*50 = $2000
Thus the remaining amount is $500.