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Calculator help - maths watch

1. a bit of a trivial question:

(-9log9 -5log5 +14log14)/14 = 0.940 does not seem to be working by not giving me 0.940.

I am pressing the log button then entering 9 afterwards , and doing the same with the others in the brackets. Probably doing it wrong, how can resolve this.

Thanks.
2. Which calculator do you have?
3. (Original post by DOJO)
a bit of a trivial question:

(-9log9 -5log5 +14log14)/14 = 0.940 does not seem to be working by not giving me 0.940.

I am pressing the log button then entering 9 afterwards , and doing the same with the others in the brackets. Probably doing it wrong, how can resolve this.

Thanks.
Are you sure you have written the question correctly? I have used logs to base 10 and natural logs and neither give the answer you require.

4. (Original post by DOJO)
a bit of a trivial question:

(-9log9 -5log5 +14log14)/14 = 0.940 does not seem to be working by not giving me 0.940.

I am pressing the log button then entering 9 afterwards , and doing the same with the others in the brackets. Probably doing it wrong, how can resolve this.

Thanks.
Unless you have a really old calculator (rather than a 2 line version) then I suspect your problem is not using enough brackets. Try:

((-9log9)+(-5log5)+(14log14))/14. That should work better. Also ensure you don't confuse log and ln.

I think you might be doing something like (alog(a +b log b ) instead of (a log a) + (b log b)
5. (Original post by Chriz M)
Unless you have a really old calculator (rather than a 2 line version) then I suspect your problem is not using enough brackets. Try:

((-9log9)+(-5log5)+(14log14))/14. That should work better. Also ensure you don't confuse log and ln.

I think you might be doing something like (alog(a +b log b ) instead of (a log a) + (b log b)
hmm this is giving me 0.28
6. (Original post by olipal)
Which calculator do you have?
casio fx-85MS
7. (Original post by DOJO)
hmm this is giving me 0.28
Where does the question come from? If from a text book are you looking at the right answer?

I think the logs are in BASE TWO

8. (Original post by steve2005)
Are you sure you have written the question correctly? I have used logs to base 10 and natural logs and neither give the answer you require.

yep written correctly, taken from a lecture slide:

entropy(9/14,5/14) = -9/14log9/14 – 5/14log5/14
= -9/14(log9 – log14) -5/14(log5 – log14)
= -9/14log9 + 9/14log14 – 5/14log5 +5/14log14
=-9/14log9 -5/14log5 +14/14log14 = (-9log9 -5log5 +14log14)/14 = 0.940 bits (fractions of bits allowed!!)
9. (Original post by steve2005)
Where does the question come from? If from a text book are you looking at the right answer?

I think the logs are in BASE TWO

Yeah, that makes sense.
Right how do you do that with a calculator.
10. If the log is to base 2, then you may not be able to do it with your calculator.

If you can, then you should have a button that's like
log[]([])

I can't really type it. It's like a log, with an empty base, and an empty whatever-goes-in-the-brackets.
11. (Original post by AnonyMatt)
If the log is to base 2, then you may not be able to do it with your calculator.

If you can, then you should have a button that's like
log[]([])

I can't really type it. It's like a log, with an empty base, and an empty whatever-goes-in-the-brackets.
Will it be possible if you could verify for me if you get that answer at a base 2? I have just tried it, I got 0.6
12. (Original post by DOJO)
Yeah, that makes sense.
Right how do you do that with a calculator.
Here is the manual that MIGHT help.

http://support.casio.com/pdf/004/GY300_Dtype_E.pdf

Or you can convert to base 2: Take log9 divided by log2 will convert to log base 2 of 9

13. (Original post by DOJO)
Will it be possible if you could verify for me if you get that answer at a base 2? I have just tried it, I got 0.6
I can confirm it!

Basically, I'm very paranoid about calculators. I don't trust them.
I overuse brackets.

I typed in:

1/14 x ((-9 x log2(9)) - (5 x log2(5)) + (14 x log2(14)))

= 0.9402859587...
= 0.940

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