Tom is going to build a fence around his garden which is a rectangle measuring 8m by 12m. he will put in post which will be 4m apart . if the post cost $4, each what will be the total cost for all the post

$40

The perimeter of the garden has length ...

... P = 8 m + 12 m + 8 m + 12 m = 40 m

Since there is a post every 4 m, there will be a total of ...

... (40 m)/(4 m/post) = 10 post

The cost per post is $4, so the total cost is ...

... (10 post)×($4/post) = $40

Alternate solutions

You can consider this several ways. One way is to look at the average cost per meter. Each $4 post is good for 4 m, so the cost of posts is ...

... ($4/post)/(4 m/post) = $1/m

Then the 40 m perimeter can be expected to require $40 in posts.

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Another way to consider this is to count the posts (and/or cost) required on each side of the garden. An 8 m side will require 2 posts, so cost $8. A 12 m side will require 3 posts, so cost $12. The sum of the costs for the 4 sides is ...

... 2(8$ +$12) = $40

Comment on fence posts

For a stand-alone fence of length 8 m, 3 posts of 4 m spacing (not 2) would be required: one at each end and one in the mddle.

Here, the sides don't stand alone. The end post of one side serves as the beginning post of the adjacent side. Hence, the total number of posts is simply the total number of 4 m sections.

its 4 because 2 times 2 is 4, if you double the number two you get four