GMAT Math

Hi there,

Could you help me to resolve this set of PS and DS ?
I am very interested by the method to resolve these

regards

First off: I believe you should try posting fewer questions per post. You have 13 questions in the document provided. You will have very few people willing to spent the time/resources to answer all of your questions in one post.


Q1 (3 of 37).
(operation)9 * (operation)6 = 3*9*3 = 9*9 = 81. This means that (operation) of x = 81. You have two options: x is either odd or even.
a. x is odd means that (operation)x = 3x = 81. This means x = 27. This solution is consistent with the initial assumption that x is odd, so when you're taking the exam you just stop here and pick D.
Answer: D.


Q2 (4 of 37)
Notice that the ratio of water:concentrate is 3:1. This means that for 4x juice you need x concentrate. You want to prepare 200 6-ounce serving, meaning 200*6 = 12*100 ounces of juice.
4 ounces juice................1 ounce concentrate
12*100 ounces juice........12*100*1/4 ounces concentrate or 12*25 ounces concentrate.
Since you have your juice in 12 ounce cans, you will need 25 such cans.
Answer: A.


Q3 (7 of 37)
Let's start by analyzing the picture. Notice that the measurement of angle ADB = 180 - 2x. Now, the measurement of angle ABD = 180 - x - (180 - 2x) = x. This means that ADB is an isosceles triangle, with AD = BD.
Now, triangle BDC is isosceles as well, since both angles D and C have the same measurement. This means that BD = BC = AD
1 will therefore be sufficient since AD = BD = BC = 6
2 is insufficient since we do not know anything about lengths, only angles.
Answer: A.

Actaully per the rules of this forum only one question is allowed per post. Like DanaJ pointed out u will get more reponses if u stuck to this format. Just a friendly suggestion.

Also browsing through your questions I see that most (may be even all) have been answered on this forum.

If u search by keywords u should be able to find. This way u dont wait for others to respond.


Regards,
CR

Q4 (8 of 37)
Say d = number of dogs, b = number of birds, t = total number of pets in the store.
You get that 1/3*t = d and that 1/5*t = b.
1. tells us that 1/5t = 30, meaning that t = 5*30 = 150. This makes d = 1/3*150 = 50 dogs. So 1 is sufficient.
2. tells us that d = b + 20. Replace d and b and you get that t/3 = t/5 + 20. Subtract t/5 from both sides and you get that 2t/15 = 20, finally getting to t = 150. d will be 1/3*150 = 50, so 2 is sufficient as well.
Answer: D.


Q5 (9 of 37)
What we should do first is transform miles into kilometers, since we're actually working with kilometers. 10 miles = 16 kilometers and now we can get started:
1. Pei was walking with an average speed of less than 6.4 km/h. This means that he walked a maximum of 8.8 km in 2 hours, which is less than 16 km. So 1 is sufficient.
2. 9 mins/km means that he would spend 16*9 = 144 minutes for the 16 km, which is more than 2 hours. So 2 is sufficient as well.
Answer: D.


Q6 (10 of 37)
Each stmt offers the same type of info: an additional point. What you should know is that if you have the slope of a line and a point on the line, it is sufficient to establish the equation of the line, meaning that you can tell if a certain point is or is not on the specified line. So either stmt is sufficient. Let me use one of the stmts to prove this.
A line's equation is y = a*x + b, with a being the slope. Since l has a slope of 3/4, then this means that l's equation will be y = 3/4*x + b.
Now, stmt 1 tells us that (4, 4) is on line l, meaning that 4 = 3/4*4 + b. This helps us find b, which will be 1. This means that l's equation is y = 3/4*x + 1.
Now we can check if (-2/3, 1/2) is on line l. If it is, then 1/2 has to equal 3/4*(-2/3) + 1, which is true.
Answer: D.

Q7 (11 of 37) - really cute one...
You are looking for (2 + 4 + 6 + ... + 20) - (1 + 3 + 5 + ... + 19) = x. My suggestion is to forget about the parenthesis and you get that:
x = 2 + 4 + ... + 20 - 1 - 3 - ... - 19.
You should notice that the difference between terms is exactly 1 in every case and pair things up, so it's easier:
x = (2 - 1) + (4 - 3) + (6 - 5) + .... + (20 - 19) = 1 + 1 + ... +1 - you have ten 1's, since there are 10 pairs of (even - odd) numbers.
Quick, simple and efficient: B


Q8 (12 of 37)
Notice that the conveyor belt is wrapped around exactly half of the circumference for each wheel. The rest of it is actually the distance between the centers of the wheels (= x). So you will have that 2x = 15 - 2*(2PiR^2/2) or that 2x = 15 - Pi (since R = diameter/2 = 1/2). This means that the distance you are looking for is (15 - Pi)/2.
Answer: A.


Q9 (15 of 37)
The info provided means that the 20th board counting from the top is the 15th counting from the bottom. You will have another 14 boards below this one, making the whole stack 34 boards high.
Answer: D.


Q10 (17 of 37)
We are trying to figure out the remainder of dividing n to 6.
1. tells us that n is a multiple of 5. This doesn't help much, except telling us that the last digit of n is either 5 or 0. Say n = 20; then the remainder will be 8. But if n = 25, the remainder will be 1. If n = 30, then the remainder will be zero. There is no way of telling what the remainder will be, so 1 is insufficient.
2. is sufficient, since 6 is a divisor of 12. If n is divisible by 12, then n is certainly divisible by 6 (since 12 = 2*6). This means that the remainder will be zero. 2 is sufficient.
Answer: B.

Q11 (18 of 37)
f(x) is provided in every case. We need to calculate f(1 - x) in every case and see if they are equal or not.
A. f(1 - x) = 1 - (1 - x ) = x - NO
B. f(1 - x) = 1 - (1 - x)^2 - NO, since you would have -2x in the way
C. f(1 - x) = (1 - x)^2 - x^2 - NO, not the same as f(x)
D. f(1 - x) = (1 - x)^2*x^2 - BINGO
Answer: D.

Guys, Many thks for your prompt reply and your advice