A shirt is on sale for $15. its original price was $25. by what percentage did the price decrease?
1 answer:
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The answer is: 
Which can be written as: [-8, infinity)
This is the interval from -8 to infinity. So -8 is our left most point on the number line and infinity being our right most. There is no boundary on the right side.
Note how the left side has a square bracket and the right side has a curved parenthesis. This isn't a typo. The square bracket tells the reader "include the endpoint -8 as part of the solution set". The parenthesis tells the reader "do NOT include the endpoint infinity as part of the solution set".
Rule: infinity and negative infinity is always paired with a parenthesis because these aren't numbers. It's impossible to reach infinity, therefore it's impossible to include it in the set of values. If you could include it, then that implies you ran out of numbers.
Which can be written as: [-8, infinity)
This is the interval from -8 to infinity. So -8 is our left most point on the number line and infinity being our right most. There is no boundary on the right side.
Note how the left side has a square bracket and the right side has a curved parenthesis. This isn't a typo. The square bracket tells the reader "include the endpoint -8 as part of the solution set". The parenthesis tells the reader "do NOT include the endpoint infinity as part of the solution set".
Rule: infinity and negative infinity is always paired with a parenthesis because these aren't numbers. It's impossible to reach infinity, therefore it's impossible to include it in the set of values. If you could include it, then that implies you ran out of numbers.