Giant Inequality QC Technique

[Jmoustafa345]

Quick question: When you use the giant (or invisible, per the text) inequality technique to compare Quantity A and Quantity B in a Quant Comp problem, what are the rulings on adding/subtracting/multiplying/dividing by a variable? There was a reason why you have to be careful with variables in giant inequalities, but I can't remember exactly what it was.

Thanks!

[n00bpron00bpron00b]

Addition/Subtraction -

If considering a particular value -
-> you are allowed to add/sub any value (positive or negative) as long as you perform the same operation on both the columns

In case of a variable
-> you are again allowed to add/sub any variable as long as you perform the same operation on both the columns

Multiplication/Division -

If considering a particular value -
"Make sure the value is strictly positive" and perform the same operation on both the columns

In case of a variable -
You need to have some evidence (given in the problem statement or logically deduced) that the variable is strictly positive - else you cannot multiply or divide by a variable on both the columns

Square and Square Root
-> Again, you can square or square root both the columns if and only if both columns are positive

[Jmoustafa345]

Thank you!

[tommywallach]

Great explanation, Noob!