True?

MSE

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Feb 28, 2021
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11
Hello! It's true?

30<a≤120.
(30<a≤120)/2.
15>a/2≥60.
 
Why did you change the direction of the "<" and "≤" ?
 
NOTE: Normally you swap the direction of inequalities only when multiplying or dividing throughout by a negative amount.
 
There is another reason to swap the direction of inequalities, which may have lead you astray.

[MATH]0 < a < b \iff \dfrac{1}{a} > \dfrac{1}{b} > 0.[/MATH]
 
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