Brain Teaser for the Geniuses???

It's 15. It's not as hard as it looks.

Double

[edit on 22-3-2007 by SpeakerofTruth]

15 is not one of the choices. The choices are:

A) 18
B) 21
C) 24
D) 31

[edit on 22-3-2007 by Shar]

This is just a guess, but I am going to guess that the answer is 24.

Okay, but you only get 3 more guesses.

Originally posted by yeahright
Okay, but you only get 3 more guesses.

How many have I made so far. Ten? Fifteen?

3 4 6 9 18 22 23 25 28 29 32 33 36 39 40 44 47 48

?? You say you have faith in the numbers? What's the pattern here? You jump from 9 to 18 and then have no large jumps ever again? This is no pattern...it's purely random. Unless you'd like to explain how you came to this....instead of saying you have "faith" in it.

However, 18 is the correct answer. I spent the afternoon on it, and this is what I came up with: (BTW...if I was taking the test I would have guessed 18 without having a clue why)

you have these numbers:

3-4-6-9-?


3x2 - 2 = 4
4x2 - 2 = 6
6x3 - 9 = 9
9x3 - 9 = 18 which is the next number in the series!


The first 2 numbers get multiplied times 2 and you subtract 2, the next 2 sets of numbers you multiply times 3 and subtract 9.

Are you serious. This is interesting. I will show my son this. If this is true we know he missed that question.

Originally posted by Shar
Are you serious. This is interesting. I will show my son this. If this is true we know he missed that question.

You don't know what the answer is? I thought you knew the answer and was just quizzing us to see if we could figure it out.

lol---Check my first post. No this was on a test my son had and he couldn't figure it out. The answers were multiple choice. Thats all I have. He thought it should of been 13. As did I when I looked at it.

All of you are wrong.

Clearly the answer is this:

Originally posted by Paresthesia
All of you are wrong.

Clearly the answer is this:

Parethesia, you are too cute.

Excitable_Boy,

My son says this is not logical. He seems to say your using just random variables. Any number can do that. Where does the 2 and 9 come from is his question?

March into the school and ask the headteacher to explain it.
And if he/she can't within five minutes, ask how they expect adolescents, who are bubbling with hormones, stuck in a test, and full of anxiety about it to get it right in a few minutes.

Originally posted by Shar
Ok this was on my sons standardized test today.

Now, he had 4 multiple choice answers which were given to him. However, I will not post those yet. Till I get a few answers and see if anyone even gets one of those answers.

In the end I don't know the answer I just have the four multiple choice answers. Which I will post later. Good Luck.

Shar, I only spent a couple of minutes on this, but I would most logically say the answer is 18 with the possible choices. If it were not multiple choice, the answer most logically would have been 13, like so many people have chosen.

Why 18 with the choices provided? Multiply the first square and the third square to reach the fifth square of 18. If there were a sixth square multiply the second square and the fourth square to reach 36. Notice that all even squares then would be numerical squares. So it basically is a multiplicative alternating series with odd and even elements.

Excitable_Boy
The first 2 numbers get multiplied times 2 and you subtract 2, the next 2 sets of numbers you multiply times 3 and subtract 9.

I'm not sure yet whether your answer is right or wrong, but I don't know why you chose to multiply the first two by 2 and the second two by 9. It seems the patern would have to stem directly from the given information in an obsious, readily distinguishable pattern.

Great Tech
Why 18 with the choices provided? Multiply the first square and the third square to reach the fifth square of 18. If there were a sixth square multiply the second square and the fourth square to reach 36. Notice that all even squares then would be numerical squares. So it basically is a multiplicative alternating series with odd and even elements.

Again, there is nothing in the pattern to indicate that they want you to multiply the first times the third and the second times the fouth. You have to jump to an unsupported conclusion to make it work.

I've been working on this one myself on and off since it popped up, but I'm really statring to think it's a typo on the answer sheet.

Originally posted by Paresthesia
All of you are wrong.

Clearly the answer is this:

That's my kind of math!!

I pick B) 21 - a spiral sequence?

Originally posted by lonewolf37

Great Tech
Why 18 with the choices provided? Multiply the first square and the third square to reach the fifth square of 18. If there were a sixth square multiply the second square and the fourth square to reach 36. Notice that all even squares then would be numerical squares. So it basically is a multiplicative alternating series with odd and even elements.

Again, there is nothing in the pattern to indicate that they want you to multiply the first times the third and the second times the fouth. You have to jump to an unsupported conclusion to make it work.

I've been working on this one myself on and off since it popped up, but I'm really statring to think it's a typo on the answer sheet.

The sequence is 3, 4, 6, 9, 18, 36, 108, 324, 1944, 11664...

The two keys are:

1) The second square (4) is the numerical square of 2. The fourth square (9) is the numerical square of 3. The sixth square (36) is the numerical square of 6, derived from the numerical square of square 2 (2) multiplied by the numerical square of square 4 (3), or (2*3)^2 = 36. The eighth square (11664) is the numerical square of 108, derived from the numerical square of square 4 (3) multiplied by the numerical square of square 6 (36), or (3*36)^2 = 11664. This can continue on indefinitely.

2) The second key is much simpler. An alternating odd sequence can be partly proven since the first square (3) times the third square (6) equals one of the answer choices (18). This can continue on indefinitely. This second key combined with the first key provides a logical answer of 18.

Shar, please provide us with the answer and proof.

[edit on 22-3-2007 by GreatTech]

[edit on 22-3-2007 by GreatTech]

My *personal* OPINION boils down to one of two possibilities:

Either GT's answer is correct...
OR
the correct answer is not available in the choices given!

(and so the mistake is not the student but the teacher!)

Furthermore, if I had to lay odds on the side of one of my own two created choices...I would not hesitate even for a moment to trust Great Tech and his knowledge/experience with numbers!

I am poet, a warrior of pen and WORD...I NEED mathematicians as friends to even out the ODDS!