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The number of distinct integer values of n satisfying 4−log⁡2n3−log⁡4n<0\frac{4-\log_2 n}{3-\log_4 n} < 0, is

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Solution

✅ Correct Answer: 47

For 4−log⁡2n3−log⁡4n<0\frac{4-\log_2 n}{3-\log_4 n} < 0, the fraction is negative when numerator positive and denominator negative OR numerator negative and denominator positive.


First, let us convert log⁡4n\log_4 n to base 2 for easier calculation:

Since log⁡4n=log⁡2nlog⁡24=log⁡2n2\log_4 n = \frac{\log_2 n}{\log_2 4} = \frac{\log_2 n}{2}

Our inequality becomes: 4−log⁡2n3−log⁡2n2<0\frac{4-\log_2 n}{3-\frac{\log_2 n}{2}} < 0

Let us substitute t=log⁡2nt = \log_2 n to simplify:

4−t3−t2<0\frac{4-t}{3-\frac{t}{2}} < 0

Multiplying both numerator and denominator by 2:

8−2t6−t<0\frac{8-2t}{6-t} < 0


Case 1: Numerator positive, denominator negative

8−2t>08-2t > 0 and 6−t<06-t < 0

t<4t < 4 and t>6t > 6

This is impossible since no number can be both less than 4 and greater than 6.

Case 2: Numerator negative, denominator positive

8−2t<08-2t < 0 and 6−t>06-t > 0

t>4t > 4 and t<6t < 6

Therefore: 4<t<64 < t < 6


Since t=log⁡2nt = \log_2 n:

4<log⁡2n<64 < \log_2 n < 6

24<n<262^4 < n < 2^6

16<n<6416 < n < 64


The integers satisfying 16<n<6416 < n < 64 are:

n=17,18,19,20,...,63n = 17, 18, 19, 20, ..., 63

Number of integers = 63−17+1=4763 - 17 + 1 = 47


Let us check with n=32n = 32 which should satisfy our condition:

log⁡232=5\log_2 32 = 5 since 25=322^5 = 32

log⁡432=52=2.5\log_4 32 = \frac{5}{2} = 2.5

Numerator: 4−5=−1<04 - 5 = -1 < 0

Denominator: 3−2.5=0.5>03 - 2.5 = 0.5 > 0

Fraction: −10.5=−2<0\frac{-1}{0.5} = -2 < 0

Answer: 47

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