brainteaser!

Don't worry Baron. I am sure they have the wrong number

 

Got it in about thirty seconds.

 

3 times. Step 1 - weigh 4 balls per side. Step 2, take the 4 balls from the heaviest side, and weigh 2 per side. Step 3, take the 2 balls from the heaviest side, and weigh 1 per side.

 

C. 36 books - non-fiction = 12, fiction = 24, hardcover = 9, paperback = 27

Initial equation -> 2/3f + 1/3nf = 1/4hc + 3/4pb
smallest common denominator is 12
Multiply by 12 -> 8f + 4nf = 3hc + 9pb doesn't match because 4nf < 10
Next common denominator = 24 -> 16f+8nf = 6hc+18pb doesn't match because 8nf <10
Next common denominator = 36 -> 24f+12nf=9hc+27pb matches because 12nf > 10 and 27pb < 30
Next common denominator = 48 -> 32f+16nf = 12hc +36pb doesn't match because 36pb > 30

 

You can do better

 

yes, I found that out afterwards... I've seen that puzzle before. Just forgot what the "trick" was....

 

Ah, thanks. It's more for programming problems, I actually think I have heard of this is site. I thought you meant more brainteaser-like, plain pen and paper problems