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Let S = {1, 2, 3, …, 2022}. Then the probability, that a randomly chosen number n from the set S such that HCF (n, 2022) = 1, is : 

(A) 128/1011 

(B) 166/1011 

(C) 127/337 

(D) 112/337

1 Answer

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Best answer

Correct option is (D) 112/337

Total number of elements = 2022 

2022 = 2 × 3 × 337 

HCF (n, 2022) = 1

is feasible when the value of 'n' and 2022 has no common factor.

A = Number which are divisible by 2 from {1,2,3.....2022} 

n(A) = 1011 

B = Number which are divisible by 3 by 3 

from {1,2,3......2022} 

n(B) = 674

A∩B = Number which are divisible by 6 

from {1,2,3........2022} 

6,12,18........., 2022

337 = n (A ∩ B)

n(AUB) = n(A) + n(B) – n(AIB) 

= 1011+ 674 –337 

= 1348 

C= Number which divisible by 337 from 

{1,........1022}

Total elements which are divisible by 2 or 3 or 337 

= 1348 +2 = 1350 

Favourable cases = Element which are neither

 divisible by 2, 3 or 337 

= 2022 – 1350 

= 672

Required probability = 672/2022 = 112/337

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