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JEE Main 202126 FebruaryEvening Shift
Exam
JEE Main
Year
2021
Date
26 February
Shift
Evening Shift
Subject
Mathematics
Chapter
Permutation and Combination

JEE Main 2021 · 26 February · Evening Shift · Mathematics · Permutation and Combination

A natural number has prime factorization given by n = 2 ^ x 3 ^ y 5...

A natural number has prime factorization given by n=2x3y5zn = {2}^{x}{3}^{y}{5}^{z}, where yy and zz are such that y+z=5y + z = 5 and y−1+z−1=56,y>z{y}^{- 1} + {z}^{- 1} = \dfrac{5}{6}, y > z. Then the number of odd divisors of nn, including 11, is:

Options

  1. A1212
  2. B66
  3. C1111
  4. D6x6x

Correct answer

A. 1212

Step-by-step solution

y+z=5y + z = 5

1y+1z=56y>z\dfrac{1}{y} + \dfrac{1}{z} = \dfrac{5}{6}y > z

⇒y=3,z=2⇒ y = 3, z = 2

⇒n=2x.33.52=(2.2.2…)(3.3.3)(5.5)⇒ n = {2}^{x} . {3}^{3} . {5}^{2} = \left(2 . 2 . 2 \ldots\right)\left(3 . 3 . 3\right)\left(5 . 5\right)

For calculating the odd divisor ofn=2x3y5z,n = {2}^{x}{3}^{y}{5}^{z}, xx must be 00.

Hence, Number of odd divisors =(3+1)×(2+1)=4×3=12= \left(3 + 1\right) \times \left(2 + 1\right) = 4 \times 3 = 12.

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