Posted by Jacob on Tuesday, December 11, 2012 at 11:15pm.
The halflife of hafnium156 is 0.025 s. how long will it take a 560 g sample to decay to onefourth it's original mass?

Chemistry  DrBob222, Tuesday, December 11, 2012 at 11:40pm
See above to one of your other screen names.

Chemistry  David, Wednesday, December 12, 2012 at 1:13am
Dr. Bob, I don't need ur criticism now!! I need your help to resolve these problems

Chemistry  DrBob222, Wednesday, December 12, 2012 at 2:49pm
I assure you there was no criticism. Those equations I gave you above will do them all. If you have further problems, please explain what you don't understand and we can help you through. You must understand that this is a help board and if we show you how to do one problem, then the others like that one can be done on your own. And for what it's worth, keeping the same screen name helps us help you faster and with better results.
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