Subject: General Aptitude · Chapter: H.C.F. and L.C.M. of Numbers · Exam: · Marks: · Difficulty:
L.C.M. of two prime numbers $x$ and $y(x>y)$ is 161. The value of $3 y-x$ is
(a)- 2
(b)- 1
(c)1
(d)2
Answer
Answer (as printed): A
Explanation
H.C.F. of two prime numbers is 1. Product of numbers $=(1 \times 161)=161$. Let the numbers be $a$ and $b$. Then, $a b=161$. Now, co-primes with product 161 are $(1,161)$ and (7,23). Since $x$ and $y$ are prime numbers and $x>y$, we have $x$ $=23$ and $y=7$. $$\therefore \quad 3 y-x=(3 \times 7)-23=-2 .$$
Explanation as extracted from the printed page; notation may be imperfect.