What is the sum of all two-digit whole numbers whose squares end with the digits 21?
2 Answers
Jul 19, 2016
200
Explanation:
A square number ending in a '1' can only be produced by squaring a number ending in a '1' or a '9'. Source. This helps a lot in the search. Quick bit of number crunching gives:
from our table we can see that
So
Jul 19, 2016
Explanation:
If the last digits of a square of a two digit number are
Now, if tens digit is
If ten's digit is
Hence, sum of all such two digit numbers is