Perimeter of a square
Finding the perimeter of a square when a side is given and finding the length of a side when the perimeter is given are the goals of this lesson
Given a square with side s, the perimeter (P) or distance around the outside of the square can be found by doing
P = s + s + s + s = 4 × s
Find the perimeter of a square when s = 3 cm
P = 4 × s = 4 × 3 = 12 cm
Notice that it is perfectly ok to do P = 3 + 3 + 3 + 3 = 12
However, it is usually easier and quicker to do 4 times 3 than adding 3 four times
Find P when s = 5 cm
P = 4 × s = 4 × 5 = 20 cm
Find P when s = 2/8 cm
P = 4 × s = 4 × 1/8 = (4/1) × (2/8) = (4 × 2)/ ( 1 × 8 )= 8/8 = 1 cm
A square has a perimeter of 12 inches. Find s
Here, given the perimeter, you are asked to find the length of a side of the square.
We know that P = 4 × s
You should replace P by 12 because that is what they gave you.
So, 12 = 4 × s
The problem becomes a
multiplication equation that you need to solve
However, you can solve this equation with mental math. Replace s by a question mark(?) and ask yourself the following:
4 times ? = 12 or 4 times what will give me 12? The answer is 3, so s = 3
The perimeter of a square is 64 cm. What is the length of one side?
Again, since P = 4 × s, we get 64 = 4 × s after replacing P by 64
Ask yourself 4 times what will give me 64? Since 4 times 16 is 64, s = 16
You don't have to guess 4 times what will give 64. You can also divide 64 by 4 to get 16
In fact, whenever you are looking for s and P is a big number, you should always divide p by 4 to get s
Notice that to get the perimeter of a rhombus, you can do the exact same thing we did above for the square.
Since just like the square, all sides of a rhombus are equal, there is absolutely no difference as far as getting the perimeter!
Therefore, P is also equal to s + s + s + s = 4 × s

Mar 14, 18 03:18 PM
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