Mary walks 4 miles north and then turns and walks 5 miles west. How far is she from her original starting point?
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Answer: Choice C) Multiplication property of inequality
The rule basically says that if you start with a < b and you multiply both sides by some positive number c, then a*c < b*c. The sign doesn't flip if you multiply both sides by a positive number.
The sign will flip if c is negative. So we'll go from a < b to a*c > b*c if c is negative.
Example 1:
1 < 5
-2 > -10 ... multiplied both sides by -2; sign flips
Example 2:
3 < 7
9 < 21 ... multiplied both sides by 3; sign does not flip
Similar rules apply to a > b,
and 
The rule basically says that if you start with a < b and you multiply both sides by some positive number c, then a*c < b*c. The sign doesn't flip if you multiply both sides by a positive number.
The sign will flip if c is negative. So we'll go from a < b to a*c > b*c if c is negative.
Example 1:
1 < 5
-2 > -10 ... multiplied both sides by -2; sign flips
Example 2:
3 < 7
9 < 21 ... multiplied both sides by 3; sign does not flip
Similar rules apply to a > b,