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Looking at trivikram's solution, it appears that having p2 = 2 is important here...

Letting p1, p2 be the two primes,

s=p1+p2
p=p1*p2

p-s=(p1*p2)-(p1+p2)
p-s=(p1*p2)-p1-p2

Since you have to subtract (p1+p2) from their product, it is important that you don't make the product too big, otherwise p-s would be too far from p1 chosen. The smallest prime number is 2, so p2=2.

In picking a number for p1, you want to pick a number that when you add 2, is the next prime number of a number in the answer choice. So that when you subtract (p1+p2) from (p1*p2) you get the number in the answer choice (p1-2).

Ummm....

Basically, you want to see if by adding 2 to a number in the answer choice, you get a prime number.

The only choice that does not meet this requirement is 119, for 119+2=121 which is divisible by 11.

What I wrote above appears pretty much an ANALYSIS of the answer rather than a mathematically justified approach to solve this problem...

I have this feeling that I'm circumventing...I know I'm heading in the right direction(?) but not quite getting there...

now make one of the prime number constant and othe variable, lets say Y=2 (prime number). we have x(2-1)-2 = X-2 now put different values of prime numbers in place of X to arrive at the solution.

now make one of the prime number constant and othe variable, lets say Y=2 (prime number). we have x(2-1)-2 = X-2 now put different values of prime numbers in place of X to arrive at the solution.

regards,

Amardeep

wow! thats cool. -)

i am wondering how to solve it within 2 minuts during test...

only analysis of the x-2 = 37, 121, 163, 353, 601 numbers could take much time ...

of course i know that 121 is not prime, but i would have to check others...

following are the basic tricks to be quicker in maths calculations:

1. take 5 pair of 3 digit numbers and multiply them. calculate your time taken per question (u need stop watch)... ideally u shouldnt take more than 21 secs per multipications ( e.g. 367*765)

following are the basic tricks to be quicker in maths calculations:

1. take 5 pair of 3 digit numbers and multiply them. calculate your time taken per question (u need stop watch)... ideally u shouldnt take more than 21 secs per multipications ( e.g. 367*765)