Jaanvi24
Can you please explain the solution for this? I'm not able to understand the underlying concept to approach this type of questions.
Bunuel
M and N are two positive integers and each of them has 20 factors. If r is the total number of prime factors of M and s is the total number of prime factors of N, then what is the maximum value of r-s?
(A) 0
(B) 1
(C) 2
(D) 6
(E) 26
For a number that is expressed as a^x × b^y × c^z where a,b,c are prime, number of factors of the number= (x+1)(y+1)(z+1)
Since both have 20 factors and we need to maximize the gap r-s, we need to maximize the number of primes in M and minimize for N
20 = 2×2×5 i.e. there can be max 3 primes (r=3) and M = a^1 × b^1 × c^4
Also, 20 can just be 20 i.e. there can be min 1 prime (s=1) and N = a^19
So max r-s = 2
Ans C