Answer:
8
Step-by-step explanation:
This question is simply the reverse of the Pythagorean theorem (the question is trying to confuse you by asking for the diameter when you could simply think of it as a right triangle). So all you would need to do is take C^2 (Pencil length^2) which is equal to 289, and minus it by B^2 (Cup height^2), which is equal to 225. This would then leave you with 64, which most would know of the top of there head to be the same as 8^2. Ergo, after square rooting 64, you find that the answer is 8
