[Guest]

this problem has been giving me trouble since i first laid eyes upon it. still unable to solve. i've come here as a last resort because the last time i had a problem from this book somebody from this forum solved it!

please include how it was solved if you figure it out.

i've attached a picture of the page from the book.

also, here is a link to the picture: http://twitpic.com/4r30sm

2

[curr3nt]

   B   

 A X C 

   D   

(A - C) / 5 = X but I do not see how it can be that. I wouldn't have guessed that without knowing the answer was supposed to be 2.

Observations:

A > C

A + B + C + D is odd when X is odd and even when X is even (This includes info from knowing the answer)

[Guest]

wow that's very interesting, and certainly nothing i've come up with so far! perhaps this thinking is a step closer to solving completely, i remain optimistic thank you!

[Guest]

I noticed that the middle term is a common prime factor of A-C and B+D'

38 - 23 = 15. Prime factors of 15 are 3 and 5

14+22 = 36. Prime factors of 36 are 2² and 3².

The common prime factor is 3.

49 - 24 = 25. The prime factor of 25 is 5².

49 + 11 = 60. The prime factors of 60 are 2² 3 and 5.

The common prime factor is 5.

21 - 11 = 10. Prime factors of 10 are 2 and 5

72 + 48 = 120. Prime factors of 120 are 2³ 3 and 5

The common prime factors are 2 and 5. 2 is the only choice given that is a prime factor.

Edited May 2, 2011 by jpf

[Guest]

   B   

A X C 

   D   

(A - C) / 5 = X but I do not see how it can be that. I wouldn't have guessed that without knowing the answer was supposed to be 2.

Observations:

A > C

A + B + C + D is odd when X is odd and even when X is even (This includes info from knowing the answer)

(B+D)/12 = x except that 72 - 48 = 24 and 24/12 = 2