The side length (in feet) of the square that is Nina's garden is √141. The four sides of the square are the same length, so add to ...
... 4×√141 = 4×11.874 ≈ 47.497
Rounding to the nearest foot, we find Nina needs 47 feet of fencing.
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The answer digit in the tenths place is less than 5, so we round down to the next lower foot.
Note that if you actually multiply 11.874 by 4, you get 47.496. When you're working a problem like this, you always want to maintain full calculator precision until the end. The number we actually used in that multiplication was 11.874342087... (my calculator carries 32 digits). The number that gets rounded is 47.4973683482.... Enough digits are shown here to show how close the number is to being rounded to 48.
If you have your calculator set to show only two decimal digits, you will get the wrong answer. Your calculator will show you 47.50, which you would appropriately round to 48.
