need a math check
Posted 14 February 2011 - 09:34 PM
I have 1ul of 10ng/ul solution, I add 19ul water to it so it is now 0.5ng/ul at 20ul total volume (where 1/20*10 = 0.5)
Next I take 2ul of the 0.5ng/ul and do a 1:5 dilution, so it is now 0.1ng/ul (where 1/5*0.5=0.1) at 10ul total volume.
But now I want more than 0.1ng/ul, so I add in 5ul more of the 0.5ng/ul. Now it's 15ul total volume, not 10ul anymore. What is the new concentration after this 5ul addition? I have that since I added 7ul total of 0.1ng/ul, it is (7/15)*0.5=0.2ng/ul. Is this correct and is there another way to do it?
Posted 14 February 2011 - 10:40 PM
Posted 15 February 2011 - 01:35 AM
Posted 15 February 2011 - 02:47 AM
i think: if you have 0.1 ng/ul at 10 ul--> is 1 ng. You add 5 ul of 0.5 ng/ul, so you add 2.5 ng. Your total is 3.5 ng at 15 ul, so 3.5/15= 0.233333 ng/ul
hi, ok so if i understand you correct, you added it in terms of how many ng is being put into the 15ul in the end.
so the first time, i added 2ul of 0.5ng/ul = 1ng into 10ul volume
then second time i added 5ul of 0.5ng/ul = 2.5ng
2.5ng+1ng = 3ng
3ng/15ul volume = 0.2333
but also my math gives the same (7/15)*0.5ng/ul = 0.2333ng/ul which i simplified to 0.2ng/ul
would like to know what others say. we get the same answer, so do both our approaches work or just an odd coincidence? thanks
Posted 15 February 2011 - 02:48 AM
Edited by molbio1234, 15 February 2011 - 02:48 AM.
Posted 15 February 2011 - 03:52 AM
I´m terribly sorry, you two are correct, I´M wrong by a bad interpretation. Sometimes is better stay in silence. I hope you two can excuse me . Thanks
Posted 16 February 2011 - 01:26 AM