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This is a naughty question. :shh: :dazed

Let's go step by step...

h(100) = (2.4.6.8......100)

There are 50 even numbers between 2 and 100 inclusive
Hence there are 50 "2s"


H(100) = 2^50 * (1*2*3*4*......*50)

and (1*2*3*4*......*50) = 50!

So => H(100) = 50!*2^50

H(100) + 1 and H(100) are consecutive numbers.

Note - two consecutive numbers are co-primes
(i.e. they don't have any common factor other than 1)


We can see that H(100) can have any number smaller than 50 as it's factor

So, H(100) + 1 can't have a factor smaller than 50

Hence choose E
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­The +1 turns a yes into a no. No sweat:

­
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­The most intuitive way to solve it, by reading the answer choice carefully, since range is given in choice, we dont need to get the exact anwer, we need a range only now, coming back to the question:
Since h(100) will have all even number till 100 in the product, it concludes that it will have multiple of all the primes till 50 in the product h(100) ie: 2*4*6*.....*100, it means no prime below 50 divide h(100) +1. hence the answer should be  x>40
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Zinsch123
I'm not taking credit for the following solution. Found it in another forum.

Two consecutive integers cannot be divisible by the same integer greater than 1.

So if we can prove that h(100) is divisible by every number smaller than 50, we proved that h(100)+1 is NOT divisible by any number smaller than 50 (besides 1).

2*4*6*...*98*100=2*(1*2*3*...*50)=2*(50!)
Hence, h(100) is divisible by every number smaller than 51. So the smallest prime factor of h(100)+1 is at least 53.
­So why is it 53 instead of 51?
Many thanks!
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lnyngayan
Zinsch123
I'm not taking credit for the following solution. Found it in another forum.

Two consecutive integers cannot be divisible by the same integer greater than 1.

So if we can prove that h(100) is divisible by every number smaller than 50, we proved that h(100)+1 is NOT divisible by any number smaller than 50 (besides 1).

2*4*6*...*98*100=2*(1*2*3*...*50)=2*(50!)
Hence, h(100) is divisible by every number smaller than 51. So the smallest prime factor of h(100)+1 is at least 53.
­So why is it 53 instead of 51?
Many thanks!
­
Check precise soluiton here:

https://gmatclub.com/forum/for-every-po ... l#p1035827
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