Total Frustration Radioactive Decay Need Fast Help

[PremedBeauty]

Total Frustration!Radioactive Decay!Need Fast Help!

Hello,

I have the link to the exercise:
http://www.sciencecourseware.org/VirtualDating/files/RC_6.php"

Here are my answers:

1. 1200
2. 2100
3.3800
4.14500
5.1125
6. 2050
7. ?

I would think (7) would be 3775, but it's not. I have been trying this for hours and cannot figure this out, please help. My head hurts...

 

[chemisttree]

I got 4175 BP.

 

[Gelsamel Epsilon]

It's 4200