Math Is Fun Forum

momofmathkid

Member

Registered: 2008-01-14

Posts: 32

How many fence posts was

OK, here is the 3rd and last problem that is stumping Mom:

Mr. Johannsen and Mr. Yan have decided to seperate their property by placing a fence along the property line.  They ordered enough fence posts so that the fence would have posts placed 8 feet apart.  However, 5 of the posts were not usable.  They were still able to put the fence up by placing the remaining posts 10 feet apart.  How many fence posts did they originally order?

Any help today is appreciated! 

Mom of Math Kid

luca-deltodesco

Member

Registered: 2006-05-05

Posts: 1,470

Re: How many fence posts was

if the fence posts were 8 feet apart, then the total length that the fence covered would be 8(n-1)  where n is the number of posts (n-1 because you have an extra post at the end to finish it off)

if there are 5 less posts, and they are seperate by 10, then the total length covered would be 10(n-6)

since they both cover the same distance you have

8(n-1) = 10(n-6)
8n - 8 = 10n - 60
2n = 52
n = 26

there were 26 fence posts at the start

---

The Beginning Of All Things To End.
The End Of All Things To Come.

momofmathkid

Member

Registered: 2008-01-14

Posts: 32

Re: How many fence posts was

Thanks but can you do it so that a 5th grader can understand?

Thanks again:):D