Last week, I focused on rate problems involving speed (if you’re looking to the answer to last week’s challenge question, scroll down to the end of this post!). This week, I’m going to shift to work-rate problems, which some students find even more challenging. You know these problems… the ones that say something ridiculous like: A cyborg can pet a kitten 150 times in 2 minutes. A ninja pets a kitten at half the rate… Read more
The Knewton Blog
Posts by Rich Zwelling
One of the most common areas of frustration for my GMAT students is rate problems. This seems a general extension of the challenges that word problems overall pose to students, but rate problems are particularly tricky. They require intensive setup and often rely on your realizing an implicit piece of information. As a basic example, suppose I tell you that two joggers run a single lap around the same track. Aaron runs at a rate… Read more
Prime Factorization: My single favorite topic on the GMAT. It’s not even a contest.
My passionate (some would say evangelical!) advocacy of prime factorization results not only from my finding prime numbers so inherently fascinating in and of themselves, but also from the plain and simple truth that prime factorization proves surprisingly useful on questions on which prime numbers aren’t even mentioned.
For example, any time you’re given a question asking about multiples and factors, you can bet that prime factorization will help you get to the answer quicker.
Case in point — this Data Sufficiency question from the Official GMAT Guide:
Data Sufficiency questions are often difficult to get used to, because they require an adjustment in your approach to math problems. When you went through math classes growing up, the end goal was always “Find the value of x” or “Find the area of this circle.” You were asked to give hard responses to these questions, and nothing mattered more than finding a definite value.
With Data Sufficiency, answering the question does not matter as much as the ability to answer the question. You are not primarily concerned with the final answer, but rather whether you have enough information to get you to that answer. For example, if you’re asked to find the value of x, and a statement tells you that 300x + 257 = 1345, you know that this statement is sufficient, because you can perform arithmetic on that equation to isolate x. Are you going to perform it? No, because it’s too complicated and you don’t need to! All you’re concerned with is whether you can find the answer.
Rich is one of Knewton’s expert teachers, and his strategies can really boost your SAT prep. — No matter how much practice you do, and no matter how much you try to anticipate exactly what SAT test day will be like, you can’t really know what it’s like until you go through it. I should know: I’ve done it a few times, both for real and as an educator. But even though there’s no way… Read more
Rich is one of Knewton’s expert GMAT teachers, but he’s also a whiz at SAT prep. — Subject-verb agreement is a fairly simple thing we all learn about early in school:Â If a subject is singular, the verb must also be singular.Â For example, in the sentence “Thomas sells clothing,” the singular noun “Thomas” is matched with the singular verb “sells”.Â It can be confusing, of course, that “sells” has an ‘s’ at the end… Read more