For all real numbers a, b, c, d, e, and f, the operation Θ is defined by the equation (a, b, c) Θ (d, e, f) = ad + be + cf. What is the value of (1,−2,3)θ(1,−1/2,1/3)?

A. -1

B. 5/6

C. 1

D. 5/2

E. 3

Correct Answer: E

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For which of the following functions is f(a+b) = f(b) + f(a) for all positive numbers a and b?

And a very challenging word problem from the Official Guide. Almost no-one gets this one on the first try but there is a somewhat simple way through it:

Tanya’s letters from the GMAT Prep tests. This one often gets GMAT tutoring students caught up in a tangled net. With combinatorics it’s important to stay practical. We’ll take a look at how to do that in the explanation:

Here’s an exponents puzzle that comes up a lot in GMAT tutoring sessions:

This is one of the most difficult questions in the GMAT universe. That said, there is a simple way to solve it that relies on a fundamental divisibility rule every GMAT studier should know:

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