Monday

September 22, 2014

September 22, 2014

Posted by **A Canadian** on Wednesday, January 23, 2013 at 11:20pm.

The answer is 9 weeks.

This is what I did, and it's clearly wrong:

tn = 7 + (n-1)13

tn = 7 + 13n - 13

tn = 13n - 6

100 = 13n - 6

100 + 6 = 13n

106/13 = n

I get a crazy decimal (8.1538....) which shouldn't be the answer...

What am I doing wrong, and how do you properly answer this question?

Thanks very much in advance!

- Math -
**Reiny**, Thursday, January 24, 2013 at 8:37amYou did just fine

it said "more than 100 mm"

so

13n - 6 > 100

13n >106

n > 106/13 or > 8.15..

So you would answer...

" the plant would be more than 100 mm in the 9th week"

check:

week 8 = t8 = a+7d = 7+7(13) = 98 , less than 100

week 9 = t9 = a+8d = 7+8(13) = 111 , more than 100

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