Help! Someone please explain the solutions to this question (1 Viewer)

[qawe]

Question: Q9biii) http://www.mediafire.com/?8dmwuzsowuntoo0

Solution: Q9biii) http://www.mediafire.com/?xuxrvbqdr3kbbbv

I dont understand why they used integration. I used the sum of a GP. Someone please get back to me before exam on Monday!

 

[OmmU]

Did you get the right answer? In the marking guidelines it says"

"Makes some progress, e.g. recognises that a summation or integral is required . . . . . . I"

 

[qawe]

Did you get the right answer? In the marking guidelines it says"

"Makes some progress, e.g. recognises that a summation or integral is required . . . . . . I"

Yes and no. I got the correct year but my R = 4.2 not 4.97, i don't know if that's just because I used a different technique, or because my/their technique is wrong.
Anyway, what does the integral mean in this situation?... ie while I *may* have done it correctly, what is the logic behind their solution?

 

[TheMathStudent]

Hope the attached file helps.

 

[qawe]

Hope the attached file helps.

thanks, just want to confirm, is summation also an appropriate method?