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The function f is defined for all ...

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by II » Fri Nov 28, 2008 12:02 pm
Hi,

I know the answer to this ... but am interested in learning about the various approaches people take to answer this one.
You thinking/logic to answer this please.

Thanks.
II
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by parallel_chase » Fri Nov 28, 2008 2:07 pm
let n= 9

F(n) = 1,2,4,5,7,8

Similarly,

if p is prime number, lets say 5
f(p) = 1,2,3,4

if p = 7
f(p) = 1,2,3,4,5,6

if p=11
f(p) = 1,2,3,4,5,6,7,8,9,10

Clearly from above pattern we can say that p-1 is the answer.

Hence A
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by cramya » Fri Nov 28, 2008 2:26 pm
I cant think of a shorter approach than what parallel chase has done by picking some primes and then getting to a genric formula.
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by logitech » Fri Nov 28, 2008 4:28 pm
ANY PRIME...is the helper in the kitchen:

P=2

f(p) = 1

A) p-1

That's it.
LGTCH
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by cramya » Fri Nov 28, 2008 4:52 pm
ANY PRIME...is the helper in the kitchen:
Similar approach to what paralle chase did. I am sure we will be checking atleast one more prime (alteast I will) to make sure it is p-1 in the real GMAT.

Like I always say different minds think differently(may be u will stop wiht just 1 and be 100% confident about it :-))

I got to play catch up for the extra 5-10 secs I took to check with one/two more primes :-)

Regards,
CR
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by II » Sat Nov 29, 2008 5:02 am
yeah .. thanks guys !
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