Webinar Demo Video on SAT Math
Welcome to Fabmarks SAT Math Prep demo for the upcoming webinar. Now we're going to look at “When to Eliminate?” and also “How to Eliminate”? Let’s move on.
Let's look at this question ?x+?9=?64?x+?9=?64,
what is the value of xx
Look at the answer choices these are all numbers
One way to eliminate the wrong answer choices and pick the right one is to assume one of the answers to be right and check whether it actually is right or not. Let’s assume one of these answer choices to be the value of x now, because that's what is actually asked. Which one would be an easy assumption to be made here is looking at root xx
we would like to have a number which is a perfect square. Let's verify 25 now.
?25+?9?25+?9 =is that equivalent to ?64?64 .
Yes, in fact, it is right. So the assumption that we have made that is c= 25
turned out to be right and that is your right answer. If it did work if this equation did hold true you will try the same with any other answer choices left, but for now the only answer choice amongst the four which was a perfect square,
Actually turned out to be the right answer also. When do you solve the questions in this process when you have numbers in the answer choices, check the answers, check which of them could fit into the
Equation, Which ever fits in the equation and makes it to a valid would be the right answer.
Let's look at another video to eliminate answer choices, another question here.
Which of the following is a graph of the equation y=2x?5y=2x?5
It's a linear equation, so the graph of that on the coordinate plane would look a line. Look at the answer choices ABCD. All of them show four lines. There's a slight difference between all of those lines. Now y=2x?5y=2x?5
is a line which is of the format y=mx+cy=mx+c
. Whose slope is equivalent to m.
So the slope of this line is 2
which is greater than zero
. A line which has a positive slope moves higher as you move from the left to the right. Now using this concept we can eliminate one of the answer choice B,
which is a line which is falling down as you move from the left of the right. All the other answer choices A, C, D have lines which moves higher as you move from the left to the right. Now let's use another concept in it one of those are two of those remaining answer choices.
Let's check were does it intersect the y-axis? How do I get the y-intercept of the line is by
Let's place x=0x=0
So its -5,
So the y intercept = (0, -5).
This is a negative y intercept
the only line which has a negative y intercept is the answer choice is D.
This (Option C) has a positive y, so this is not a right answer.
This (Option A) also has a positive intercept this is also not all right answer and there are two concepts that we have used to eliminate made the three wrong answer choices:
- The Y-intercept concept and
- The slope positive/ negative concept.
so one to eliminate answer choices is to use concept.
Let’s move to learn another way to eliminate the answer choices. The total area of a costal city is 92.1 square miles. Let’s note down that. The total area of a coastal city is 92.1m2m2
of which 11.3 square miles water. If the city had a population of 621,000, total population of the city is given to you as 621,000.
Which of the following is the closest to the population density in people per square mile of land area? So what we are first concerned about is how much is the land area which is got by subtracting the sea area or water area
from the total area.
Land area is equivalent to an 92.1m2?11.3m2=80.8m292.1m2?11.3m2=80.8m2.
Now what we are now calculate. Is the Population/m2m2= 621,000 / 80,
which is not going to be an easy calculation. This incase in the non calculator section, it’s going to take time to do this, but then generally these kind of questions are again the calculator section, but then don't pull out your calculator for every simple calculation. The calculations like these can be escaped if you try approximating things. Let's approximate the numerator let's like 620,000 and the denominator to about 80, if the numerator was a hundred then this would be around 6200. If it was hundred then it would turn out to be you can have 262,000 / 10, which is 6200, but the new denominator is less than a 100
, so the fraction 62,000 / 8 will be definitely greater then 6200 and it's not going to be definitely as biggest 55,000 or 76,000. It's going to be one of these two. The nearest to this 6200 happens to be 6740 if you wanted to verify little more. Try cancelling out unit in the denominator 6?8=486?8=48
only. So the first digit of the answer has to be seven, so that is enough for you to pick. B
as you're right answer and what we have tried to explain you here is, don't spend time in pulling out your calculator for each and every calculation that you find on the test. Sometimes it is easy to approximate things and just escape all the calculations in the solutions and save time in doing so.
Right, let's move on to understand another way to eliminate your answer choices. Okay here's a question where we don't eliminate answer choices. We could answer choices then we'll try doing it in two ways. You eliminate and you don’t eliminate. Now, finding answers to be numbers we can try eliminating using assumption of one of them to be right. Let's assume Option B
to be right now. What is asked in this is?
There is a quadratic equation 2x2?4x=t2x2?4x=t,
You are asked to find the value of t
. You're given that this equation has no real solutions. This is of the format in ax2+bx+c=0ax2+bx+c=0.
A quadratic equation which would have non-real roots, if b2b2-4ac< 0.
If i put -1
as in the place of t,
then this equation will turn to be
in this case b2b2-4ac
going to be 16.
16-8, which in fact > 0, what we're looking for is
as for this is less than zero, this cannot be right. Now let's look at something else. Let's verify C
now. If it was one the value t
will be 2x2?4x?1=0"2x2?4x?1=0",
which is 16+8, which is again greater than 0.
This is the value of b2b2-4ac this
not again going to be the right answer. Now similarly you can do the same process and say this is also not right (option D
). This in fact is right. This was way to eliminate the wrong answer choices and get your right answer.
Else you could have done no elimination and applying the concepts which is the traditional Math Method: b2b2-4ac
for this equation would be (?4)2?4(2)t<0(?4)2?4(2)t<0,
which gives the equation us an equation 8t<-16
, which implies t<-2. N
ow the only answer choice is less than -2
in the given options is minus -3.
Again it is the answer choice A.
When there are certain questions where you can apply the
concept and get the right answer, apply the concept and get your right answer. certain questions become simpler when you try to eliminate the wrong answers and get your right answers.
Thank you so much.
Hi guys this is Alexiar from Fabmarks. I hope you like our first exclusive preview of our upcoming Webinar. Well there are no secrets and strategies to score high in SAT will be covering those secrets and our upcoming webinar, this Friday on 28 October. So if you are SAT test taker, you need to be there. So go ahead and register now.