Foo - Can you solve this math problem?

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View Full Version : Can you solve this math problem?

Yan
04-18-10, 08:26 AM
I can't figure this out and I feel stupid. Help me out here:

Multiple choice, no calculator allowed:

If [2^x]-[2^(x-2)]=3(2^13), what is the value of x?

a) 9
b) 11
c) 13
d) 15
e) 17

The answer is d, but how do you solve this without a calculator?

edit: Nevermind, got it.

Siu Blue Wind
04-18-10, 10:25 AM
f) 42

jsharr
04-18-10, 10:47 AM
I try not to put a value on x. Last time I did, he thought it was a bounty and he turned himself into me. I thought he would never leave, and it cost \$75 bucks.

phantomcow2
04-18-10, 11:56 AM
Usually when your variable (x) is a in exponent form, you take the natural log of both sides. Recall (hopefully) the handy power of logs:

If you take the log of a^x, where a is a constant, the x goes in front. This results in x(ln(a)). Take the logs of both sides and you'll probably find ln(2) cancels or something.

phantomcow2
04-18-10, 11:56 AM

Dan The Man
04-18-10, 01:46 PM
I can't figure this out and I feel stupid. Help me out here:

Multiple choice, no calculator allowed:

If [2^x]-[2^(x-2)]=3(2^13), what is the value of x?

a) 9
b) 11
c) 13
d) 15
e) 17

The answer is d, but how do you solve this without a calculator?

edit: Nevermind, got it.

3(2^13) is (0.75*2*2)*2^13. That is 0.75*2^15. Easy stuff. 2^(x-2) is going to be 1/4 the value of 2^x right. So 3/4 of 2^x equals 3/4 of 2^15. Guess what x equals.

Snicklefritz
04-18-10, 02:11 PM
Where did you find this question?

Gilla Gorilla
04-18-10, 08:15 PM
here's another question for you: Whats the integral of 2xdx between 10 and 13?
=P

recon455
04-18-10, 09:39 PM
here's another question for you: Whats the integral of 2xdx between 10 and 13?
=p
69.
Ha
ha
ha.

phantomcow2
04-18-10, 09:47 PM
69.
Ha
ha
ha.

no credit without work:
F(x) = x^2
F(b) - F(a) = 169-100=69

alexvpaq
04-18-10, 11:38 PM
I prefer chemistry class GO PV=nRT!

UmneyDurak
04-18-10, 11:42 PM
here's another question for you: Whats the integral of 2xdx between 10 and 13?
=P

I used to remember how to do that. :lol:

fantom1
04-20-10, 05:40 PM
math is the devil.

deraltekluge
04-20-10, 06:19 PM
Young man, in mathematics you don't understand things. You just get used to them.
~John von Neumann (http://en.wikipedia.org/wiki/John_von_Neumann)~