Defined Functions

[xerocoool]

Hi,

1) For any positive integer N, pi (N) represents the number of factors of N inclusive of 1 and number itself. "a" and "b" are prime numbers

Col A: pi (a) + pi (b)
Col B : pi (a*b)

If we take "a" as 2 and "b" as 3

Col A : pi (2) + pi (3) = 4 ( 2 and 3 each have 2 factors)
Col B : pi (6) = 4 factors

Both equal

Case 2:

a = 2 b = 2
Col A : 4
Col B : Answer given in the book is "4" ?

That's an error right ? 4 has 3 total factors (including 1 and number itself).

So the answer must be "D" and not "C".

Just wanted to confirm :)

Thanks
Xero

[asishkm]

Yes, you are certainly correct.

Even I thought initially the answer would be (C).

However, nowhere does it mention that 'a' and 'b' are different prime numbers.

If they are the same, then a*b = a*a has only 3 factors, 1, a, a*a.

So, the answer will be (D).

Thanks for helping me out as well. :)

[xerocoool]

Hi Asish,

It has not been mentioned that both "a" and "b" are different. Thanks for the confirmation :)

Xero

[tommywallach]

Absolutely right. This isn't from one of our books is it?

-t

[xerocoool]

nope. Princeton I guess

[tommywallach]

Phew! : )