February 20th, 2013, 10:40 AM  #1 
Newbie Joined: Jan 2013 Posts: 5 Thanks: 0  ppm and powers?
Hi would anyone be able to give me a bit of advice? How do you convert very large powers of 10 into percentages? I do not fancy wring 5.20 x 10^21 out by hand and working backwards from that. Surely there is a perfectly simple solution but i can not see it. I was thinking along the lines of division being the opposite of multiplication, could I divide 10^21 by itself to cancel out? The information I am given to work with involves a total of number of something times 10 to a power 25 of molecules m^3 of atmosphere, and something times 10 to power of 21 as a one of the gasses. I am then asked to work out the concentration of this gas in parts per million. Would be really grateful if someone could point me in the right direction. 
February 20th, 2013, 12:28 PM  #2 
Global Moderator Joined: May 2007 Posts: 6,806 Thanks: 716  Re: ppm and powers?
Give a more precise description.

February 20th, 2013, 01:13 PM  #3 
Newbie Joined: Jan 2013 Posts: 5 Thanks: 0  Re: ppm and powers?
I am worried to put the exact question because last time I did that someone gave the full answer. I can not learn by people doing my work for me, I need to work it out for myself, I am just looking for a nudge or two in the right direction. it comes down to this really, a calculator will not give you such a large power in digits, one could write the thing out but to write 10 to the power of 21 is an inefficient way to do things. I can only think that something by 10 to the power of 21 needs to be simplified somehow, in order to get it as a fraction of a percentage. Once it is at a fraction over 100% I know what to do. Getting a number n times 10 to the power of 21 in a format I can present it as a fraction over 100 is the name of the game. 
February 21st, 2013, 12:53 PM  #4 
Global Moderator Joined: May 2007 Posts: 6,806 Thanks: 716  Re: ppm and powers?
Since the question is very fuzzy, the only thing I can suggest is to take the large power of ten outside the work on the calculator and put it back in at the end.

February 24th, 2013, 07:39 AM  #5 
Newbie Joined: Jan 2013 Posts: 5 Thanks: 0  Re: ppm and powers?
blimey! if the question is too fuzzy for you guys I don't know how I'm gonna do it.. the question relates to molecules of gas in the atmosphere. The information given is that there are for example 2.4 x 10^25 of molecules m^3 in the atmosphere. I am then given a number of one of the gasses which has a concentration of n.n X 10^21. I am then asked what the concentration of gas is in parts per million. Now once I have a percentage I can work out parts per million. The thing I am struggling with is how to get those massive powers into percentages. I seem to have passed all other questions on the test. I could leave this one and still get a decent mark but that's not the point. I must understand this. 
February 24th, 2013, 07:41 AM  #6  
Newbie Joined: Jan 2013 Posts: 5 Thanks: 0  Re: ppm and powers? Quote:
 
February 24th, 2013, 11:45 AM  #7 
Global Moderator Joined: May 2007 Posts: 6,806 Thanks: 716  Re: ppm and powers?
I am guessing you want to divide a.10^21 by b.10^25. In that case you have (a/b)10^4. Can you handle that?


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