( 1 0 n ) % ÷ ( n 1 0 ) % = 1 0
What is the integer value of n satisfying the equation above?
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I forget to say that it needs to be rational, and lo g ( n ) need to be rational too. In fact all logarithms in base ten, except the powers of ten is irrational.
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Ah, I see your point now, that's a nice way to put it.
Just curious, do you have a proof for your claim
For lo g 1 0 n to be rational, where n is an integer, n must be an exponent of base 1 0 , that is n = 1 0 k for some integer k
I find your logic to be flawed. n − 1 is an integer, but that does not mean that 1 0 n − 1 is an integer, so why must lo g 1 0 n be an integer?
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Rewriting this equation as fractions:
( 1 0 n ) % ÷ ( n 1 0 ) % = 1 0 ⇒ 1 0 0 1 0 n ÷ 1 0 0 n 1 0 = 1 0
1 0 0 1 0 n ÷ 1 0 0 n 1 0 = 1 0 0 1 0 n ⋅ n 1 0 1 0 0 = 1 0
n 1 0 ⋅ 1 0 2 1 0 n ⋅ 1 0 2 = 1 0
n 1 0 1 0 n = 1 0
1 0 n = 1 0 ⋅ n 1 0
1 0 n − 1 = n 1 0
lo g n 1 0 = n − 1
1 0 ⋅ lo g n = n − 1
lo g n = 1 0 n − 1
We are looking for a positive integer, which one is n . If n is a integer, then n − 1 is a integer, which means that lo g n is rational because 1 0 n − 1 is rational too. With these restrictions, the only possible numbers for n is powers of 10. But 10, 100, 1000 or higher, aren't solutions for this equation. Then, 1 is the only number that satisfies these conditions, and lo g 1 = 0 , which works when 1 0 n − 1 = 0 .
Then the answer is 1 .