Difference between revisions of "2018 UNCO Math Contest II Problems/Problem 4"
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== Solution == | == Solution == | ||
− | We can use [[complementary counting]]. Taking the prime factorization of <math>36,000,000</math>, we get <math>2^8\cdot3^2\cdot5^6</math>.So the total number of factors of <math>36,000,000</math> is <math>(8+1)(2+1)(6+1) = 189</math> factors. | + | We can use [[complementary counting]]. Taking the prime factorization of <math>36,000,000</math>, we get <math>2^8\cdot3^2\cdot5^6</math>.So the total number of factors of <math>36,000,000</math> is <math>(8+1)(2+1)(6+1) = 189</math> factors. Now we need to find the number of factors that are perfect squares. So back to the prime factorization, <math>2^8\cdot3^2\cdot5^6 = 4^4\cdot9^1\cdot5^3</math>. Now we get <math>(4+1)(1+1)(3+1)=40</math> factors that are perfect squares. So there are <math>189-40=\boxed{149}</math> positive integer factors that are not perfect squares. |
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− | Now we need to find the number of factors that are perfect squares. So back to the prime factorization, <math>2^8\cdot3^2\cdot5^6 = 4^4\cdot9^1\cdot5^3</math>. Now we get <math>(4+1)(1+1)(3+1)=40</math> factors that are perfect squares. | ||
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− | So there are <math>189-40=\ | ||
~Ultraman | ~Ultraman |
Latest revision as of 14:34, 2 June 2023
Problem
How many positive integer factors of are not perfect squares?
Solution
We can use complementary counting. Taking the prime factorization of , we get
.So the total number of factors of
is
factors. Now we need to find the number of factors that are perfect squares. So back to the prime factorization,
. Now we get
factors that are perfect squares. So there are
positive integer factors that are not perfect squares.
~Ultraman
See also
2018 UNCO Math Contest II (Problems • Answer Key • Resources) | ||
Preceded by Problem 3 |
Followed by Problem 5 | |
1 • 2 • 3 • 4 • 5 • 6 • 7 • 8 • 9 • 10 | ||
All UNCO Math Contest Problems and Solutions |