For every integer a1, a* is defined as the least prime factor of a.

Question

For every integer a>1, a* is defined as the least prime factor of a. Is b*<c*?

1. b is an odd integer greater than 1
2. c is an even integer

LevanKhukhunashvili · Answer

1 stm --> b is odd and we dont know anything about c;  insuff 
2 stm --> c is even, so the least prime factor of c is 2. 2 cant be greater than any prime;  suff

P.S Honestly I dont like the wording of the question

IMO
Ans:  B

fireflyejd1 · Answer

Statement 1: B is odd
 Even if B is an odd number, C can be an odd number of a higher or smaller maginitude containing a superior on inferior prime number. Or it can be another even n umber. We do n ot know. Insufficient.

Statement 2: C is even

Ok, since C is even, B can either be even or odd. The only possible outcome is for b is to be either equal to or greater than c. In no possible way can it ever be smaller than c. Solved.

ANSWER: B

ccooley · Answer

When they define a weird function like this one, it's not a bad idea to jot down a couple of examples before you start, just to make sure you understand what they're telling you.

For instance, here, we'd quickly calculate x* for a couple of different values of x.

If x is prime, then x* is just equal to x itself, since it doesn't have any smaller prime factors.

If x = 10, then x* = 2.

If x = 15, then x* = 3.

You might notice, at this point, that whenever x is even, x* should equal 2, because 2 is a prime factor of every even number and 2 is the smallest prime number. The words even and odd in the statements also give a clue that you should be thinking about how even and odd numbers behave differently from each other.

Statement 1 : b is an odd integer greater than 1. We already tried the example of 15; if b = 15, then b* = 3. c* could be smaller than this (for example, if c = 2, then c* = 2, which is less than 3.) Or, c* could be bigger than this (for example, if c = 7, then c* = 7, which is more than 3.) Therefore, this statement is insufficient.

Statement 2 : As discussed above, this one tells you that c* = 2.

The question asks whether b* is less than c*. Since 2 is the smallest prime number, 2 is the smallest value that b* could possibly have. b* definitely can't be  less  than 2. (Remember that 1 isn't prime.)

Therefore, the answer to the question is 'no' - since c* = 2, b* definitely is NOT less than c*. This statement is sufficient.

The answer is B.

fireflyejd1 · Answer

In the case of this question, should we not consider the possibility that b can be EQUAL to c OR GREATER than c? In which case, the option is insufficient as we will have 2 answer options at hand..?

NerdatroN · Answer

As the OA is currently diverging from the opinion of several posters it would be most helpful if a moderator could settle the matter once and for all.

Please: chetan2u Bunuel help us, you are our only hope!

chetan2u · Answer

Hi Answer is B

1) b is odd so least possible value of b* is 3 and b could be anything greater than 2, and also c can be anything and so c* could be 2,3,5,7 etc..insuff 2) c is even so c* is surely 2. Now whatever be the value of b, answer will always be NO For example say b is also even so b* is 2, we are then looking for is b*

bumpbot · Answer

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For every integer a>1, a* is defined as the least prime factor of a.

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