Question

How many 4 digit numbers can be written as difference of squares in at least one way ?___

Answer 1

Option (d)

All numbers of the form 4k+2 cannot be expressed as difference of squares.

Thus, those 4 digit numbers which can be expressed as difference of squares in atleast one way= number of four digit numbers - 4 digit numbers of the form 4k+2

= 9000 -2250= 6750.