Spyros13 Posted February 12, 2011 Share Posted February 12, 2011 i have this : 15,76=0.43*(20)n i have to calculate n... 15.76/0.43=20n 36.65=20n n=log2036.65 is this right??? Link to comment Share on other sites More sharing options...
hypervalent_iodine Posted February 12, 2011 Share Posted February 12, 2011 No, it isn't right. Remember this rule: log ab = b * log a Link to comment Share on other sites More sharing options...
Spyros13 Posted February 12, 2011 Author Share Posted February 12, 2011 (edited) but is this steps right? 36.65=20n => =>n=log2036.65 Edited February 12, 2011 by Spyros13 Link to comment Share on other sites More sharing options...
Blahah Posted February 12, 2011 Share Posted February 12, 2011 (edited) but is this steps right? 36.65=20n => =>n=log2036.65 No, this step is incorrect. you have 36.65=20n first put the unknown on the left: 20n = 36.65 to get rid of the exponent you can take the log of 20n. Make sure you do the same to both sides. n log20 = log36.65 then you should be able to find n. Edited February 12, 2011 by Blahah Link to comment Share on other sites More sharing options...
Shadow Posted February 12, 2011 Share Posted February 12, 2011 (edited) hypervalent_iodine and Blahah, you are both incorrect. Spyros, you're answer is correct; the guys above didn't notice you took the base 20 logarithm of both sides, not the natural/base 10 log: [math]36.65 = 20^n[/math] [math]\log_{20}(36.65) = \log_{20}(20^n)[/math] [math]\log_{20}(36.65) = n \cdot \log_{20}(20)[/math] [math]n = \log_{20}(36.65) \approx 1.202181[/math] Edited February 12, 2011 by Shadow Link to comment Share on other sites More sharing options...
Blahah Posted February 12, 2011 Share Posted February 12, 2011 (edited) Whoops sorry - Shadow's right, I didn't notice that yours was log base 20. However, I think my solution is still correct as well. eidt: ugh, I also formatted the text wrongly in my answer. Corrected now. Maybe I should wait until I'm better at maths before advising others! Edited February 12, 2011 by Blahah Link to comment Share on other sites More sharing options...
hypervalent_iodine Posted February 12, 2011 Share Posted February 12, 2011 and this is why I'm a chemist. Link to comment Share on other sites More sharing options...
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