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Post subject: Official Guide: Problem Solving - question #1

Expert replies
by stilite » Sun Oct 18, 2009 9:51 am
If anyone has their OG 12 book handy, I'd like to know if there is a shortcut to solving any problem related to #148 in the Problem Solving section (page 173).

I get about half-way through the simplification/factoring of the initial formula, but then the "official answer" explains further steps to take that I simply/honestly never would have thought of - especially in a 2-minute time allotment.


In other words, how can I tackle such questions that give you three variables,...then tack on a "x < y" expression....and then list integers as the answers?

Many thanks....
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Source: — Problem Solving |

These kind of variable questions should be answered backwards, i.e. use the answer choices to answer the question.

The equation can be simplified as:
==> 10(x+2y)=k(x+y)

Start by plugging in the value of C (i.e.15). You will see that the equation solves to x=y. But, the question stem says that x<y. So, this and any value less than 15 cannot be the answer. Plugging in the value of D (i.e. 18), you get y=4x. This is very much possible. Check with the value of E & you will get 2x+y=0. This means that x or y has to be a negative value, but they are positive numbers (according to the question stem).

So, D is the answer.
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