Today’s post, inspired by the SAT Question of the Day for 3/11/12 offers us another opportunity to remind you of one of the few remaining truly magical test-taking techniques: Plugging In!
Plugging in is one of the best ways to take advantage of any multiple choice question involving algebra. It offers us the opportunity to avoid algebra and use numbers to solve the exact same questions. By avoiding the algebra we are able to circumvent the machinations of the test writers and eschew the traps they set for the unwary.
Quick tips about plugging in:
When to plug in
On of the most important things to learn is when you can and when you can’t plug in. If you can’t identify plugging opportunities than knowing the great technique won’t help you at all! Here is when you do it:
1. Anytime you have variables in the answer choices
2. Anytime you have the burning desire to create an algebriac equation
3. Anytime you have unknowns in the questions and fractions or percents in the choices
How to plug in
In order to plug in you must do 3 simple things:
1. Replace the unknowns in the question with a value that works easily in the problem.
2. Solve t he problem using the numbers rather than the variable
3. Write down what number is your answer
4. Replace the variable in the answer choices with the values you assigned it until you have the number you wrote down in 3.
If you follow the steps above, every SAT question and every multiple choice algebra question will get easier. Plugging in is so useful that we’d go so far to say that if your tutor or course doesn’t bring up plugging in than you should run away screaming because that’s not a real test prep class!
Now to apply this new found power to the tough question above. The first thing to recognize is that you are looking for the formula that works to give each value in the sequence so n represents the position in the sequence not the value (meaning for the first time n = 1 not 8). If we keep this in mind we can simply test out the equations and figure out which works. Another important tip here is to remember that the SAT rarely, if ever, gives useless numbers, so since they gave three values in the sequence it’s safest to test several of them before you decide a choice is valid. Let’s check that out:
If we tried the first term that means n = 1
(A) is 2(1) + 6 = 8
thus this choice is possible and we should keep trying (choices (B), (C), and (D) also work), because (E) gives us 6(1) + 5 (or 11) it does not give us 8 as it should and is thus not possible so eliminate (E).
If we try the third term than n = 3.
(A) 2(3) + 6 does not equal 14 so eliminate
(B) 3(3) + 5 DOES equal 14 so KEEP
(C) 5(3) + 3 does not equal 14 so eliminate
(D) 6(3) + 2 does not equal 14 so eliminate
(E) was already eliminated so there is no need to try it again.
Now with a little easy plugging you get correct a question that ostensibly only 44% of the kids in the world get right! Remember to plug in on the SAT! Good luck and for more tips check out our classes and free online information sessions.