Hello, I just had a quick question. I'm having issues with this problem (will attach picture in a bit). I feel like I'm using the correct formula, but I keep getting an incorrect answer. May someone look at my steps to see what I am doing wrong? Thank you in advanced!

Question

anonymous · Answer

attachment

anonymous · Answer

$$\ln (0.63)=-\Lambda*13$$

anonymous · Answer

I first set it up like this which I am sure is correct.

anonymous · Answer

$$-0.462=-\Lambda*13$$

anonymous · Answer

$$-0.462\div-13=\Lambda $$

anonymous · Answer

0.0355=lambda 
then I input it in the equation 
$$T1/2=0.693\div \Lambda $$

anonymous · Answer

and I got 19.5 years. But  I still keep getting it wrong. Can someone help me?

anonymous · Answer

$$t = \frac{ -T_{1/2} }{ \ln(2) }\ln(\frac{ N }{ N_{o} })$$t = 13 years
N/No = 0.37 (63% is gone, therefore 37% left)

This yields T_{1/2} in years:$$T_{1/2} = 9.06$$

anonymous · Answer

Oooh! Oh wow, thank you so much! I was just wracking my brain over this. Much appreciated! ^_^