Calculate the number of irreducible proper fractions

MathematicsNumber TheoryMedium

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189. $A = EKOB(36; 60; 84)$ olarsa, məxrəci A olan ixtisar olunmayan düzgün kəsrlərin sayını tapın. A) 36 B) 72 C) 144 D) 288 E) 576

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Step 1

Hi Yusif, let's solve this problem together. We need to find the number of irreducible proper fractions with a denominator equal to the least common multiple of 36, 60, and 84.

Problem Setup

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Step 2

First, let's find the least common multiple, or LCM, of the numbers 36, 60, and 84 by prime factorizing them.

$$36 = 2^2 \cdot 3^2$$
$$60 = 2^2 \cdot 3^1 \cdot 5^1$$
$$84 = 2^2 \cdot 3^1 \cdot 7^1$$
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Step 3

To get the LCM, we take each prime factor raised to its highest power present in these factorizations.

$$A = 2^2 \cdot 3^2 \cdot 5^1 \cdot 7^1$$
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Step 4

Calculating this, we have 4 times 9 times 5 times 7, which equals 1260.

$$A = 1260$$
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Step 5

Now, we need to find how many proper fractions with denominator 1260 are irreducible. A fraction is irreducible if the numerator and denominator share no common factors.

Counting Irreducible Fractions

$$n < 1260$$
$$\gcd(n, 1260) = 1$$

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About This Question

Subject
Mathematics
Topic
Number Theory
Difficulty
Medium
Question Type
Multiple Choice

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