Example: "boxes approximately 20 kg in mass are allowed"
If your box is exactly 20 kg ... will certainly that be allowed or not?
It isn"t really clear.
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Let"s check out exactly how to be precise around this in each of three popular methods:
Inequalities The Number Line Interval Notation
Inequalities
With Inequalities we use:
> greater than≥ better than or equal to much less than≤ less than or equal to
Like this:
Interval Notation
In "Interval Notation" we just compose the beginning and finishing numbers of the interval, and use:
< > a square bracket once we want to
include the end worth, or( ) a round bracket as soon as we
don"tLike this:
Number Line
With the Number Line we draw a thick line to present the worths we are consisting of, and:
a filledin circle as soon as we want to encompass the finish worth, oran open circle as soon as we don"t
Like this:
Example:
suggests all the numbers in between 0 and also 20, carry out not encompass 0, however do encompass 20
 From 1   To 2 
 Including 1  Not Including 1   Not Including 2  Including 2 
Inequality:  x ≥ 1 "higher than or equal to"  x > 1 "higher than"   x "less than"  x ≤ 2 "much less than or equal to" 
Number line:   1" width="70" height="55" />   , and not incorporate 2:
Inequality:  x ≥ 1 and x or together: 1 ≤ x  Number line:  That means as much as and including $10. And it is fair to say all prices are more than $0.00. As an inequality we display this as: Price ≤ 10 and also Price > 0 In fact we could combine that into: 0 (0, 10>
Example: x better than, or equal to, 3: <3, +∞)
Example: x ≤ 2 or x >3On the number line it looks choose this: And interval notation looks prefer this: (∞, 2> U (3, +∞) We offered a "U" to suppose Union (the joining together of two sets).
Note: be careful via ineattributes choose that one. Don"t try to join it into one inequality: 2 ≥ x > 3 wrong!that doesn"t make feeling (you can not be much less than 2 and also greater than 3 at the very same time). 
Union and also IntersectionWe just witnessed how to join two sets utilizing "Union" (and the symbol ∪). There is likewise "Intersection" which suggests "has to be in both". Think "wright here perform they overlap?".
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The Intersection symbol is an upside down "U" prefer this: ∩
Example: (∞, 6> ∩ (1, ∞)The initially interval goes up to (and including) 6 The second interval goes from (however not including) 1 onwards.
The Intersection (or overlap) of those two sets goes from 1 to 6 (not consisting of 1, consisting of 6): (1, 6>
Footnote: Geometry, Algebra and SetsYou may not have actually noticed this ... yet we have actually actually been using:

