2009 AMC 10A Problems/Problem 5
Problem
What is the sum of the digits of the square of ?
Solution
Using the standard multiplication algorithm, whose digit sum is
Solution 2
Note that:
We see a pattern and find that whose digit sum is
Solution 3
You can see that can be written as
, which is . We can apply the same fact into 111,111,111, receiving whose digits sum up to
See also
2009 AMC 10A (Problems • Answer Key • Resources) | ||
Preceded by Problem 4 |
Followed by Problem 6 | |
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