# Why is 9 involved in this problem instead of 3?

So, lets say it costs $1.25 per square yard to paint a wall. The wall is 18x25 feet. How much will it cost to paint the wall. First, I don't understand what is better. Converting 18x25 feet into yards which is (54x75) or converting down the cost from yard to feet which is aprox$0.416.

But lets say that it's better to convert feet to yards in this situation.

X is the cost.

X=((54*75)/9)*1.25

But again. There are 3 feet in a yard, and it looks like that 9 is squared. But I fail to understand why it's that way.

Can anyone explain? Thanks!

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Tip: Draw a picture of the situation – Listing May 20 '11 at 10:09
Dimensional analysis (i.e., "check your units") is a good idea even in mathematics. – ShreevatsaR May 20 '11 at 10:34