Having Birthday On Leap Day
Since Ajay celebrates his birthday on 29th February, he used to deposit Rs.500 in saving box once in 4 years. From age 20 to 60, he celebrated only 10 birthdays saving only 500 x 10 = 5000.
But Vijay withdrawing Rs.100 every year means he took 100 x 40 = 4000 so far.
That's why only 5000 - 4000 = 1000 left in the box.
