GMATPrep Questions
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Hi fourteenstix,
It's normally best to list just 1 question per post, but I'll answer both questions here:
First, the probability question. This question has LOTS of details that you have notice if you're going to answer it correctly. You'll notice that the answers have 8 as a common denominator (this provides an interesting hint to how the "math" will work. You should also notice that the question stem asks you to consider the numbers from 1 to 96, inclusive (and it's interesting that 96 is a multiple of 8...).
The prompt asks you to think about (n)(n+1)(n+2), so you'll be dealing with 3 consecutive integers multiplied together. For a number to be divisible by 8, it must include at least three 2's when the number is broken down using prime factorization:
For example: (1)(2)(3) = 6 which is NOT divisible by 8 (obviously), but you'll notice that there's just ONE 2.
For example: (2)(3)(4) = 24 which IS divisible by 8; you'll notice that there ARE THREE 2s (the 2 has one and the 4 has two).
So, we're looking for all the options that have three 2s in them...
Any option that is (even)(odd)(even) will include three 2s
Any option that has (odd)(multiple of 8)(odd) will also include three 2s
If you consider the first 8 possibilities
(1)(2)(3) = NO
(2)(3)(4) = YES
(3)(4)(5) = NO
(4)(5)(6) = YES
(5)(6)(7) = NO
(6)(7)(8) = YES
(7)(8)(9) = YES
(8)(9)(10) = YES
5/8 are what we're looking for. This pattern continues through every "set of 8", so the final answer is D
GMAT assassins aren't born, they're made,
Rich
It's normally best to list just 1 question per post, but I'll answer both questions here:
First, the probability question. This question has LOTS of details that you have notice if you're going to answer it correctly. You'll notice that the answers have 8 as a common denominator (this provides an interesting hint to how the "math" will work. You should also notice that the question stem asks you to consider the numbers from 1 to 96, inclusive (and it's interesting that 96 is a multiple of 8...).
The prompt asks you to think about (n)(n+1)(n+2), so you'll be dealing with 3 consecutive integers multiplied together. For a number to be divisible by 8, it must include at least three 2's when the number is broken down using prime factorization:
For example: (1)(2)(3) = 6 which is NOT divisible by 8 (obviously), but you'll notice that there's just ONE 2.
For example: (2)(3)(4) = 24 which IS divisible by 8; you'll notice that there ARE THREE 2s (the 2 has one and the 4 has two).
So, we're looking for all the options that have three 2s in them...
Any option that is (even)(odd)(even) will include three 2s
Any option that has (odd)(multiple of 8)(odd) will also include three 2s
If you consider the first 8 possibilities
(1)(2)(3) = NO
(2)(3)(4) = YES
(3)(4)(5) = NO
(4)(5)(6) = YES
(5)(6)(7) = NO
(6)(7)(8) = YES
(7)(8)(9) = YES
(8)(9)(10) = YES
5/8 are what we're looking for. This pattern continues through every "set of 8", so the final answer is D
GMAT assassins aren't born, they're made,
Rich
Last edited by [email protected] on Mon Sep 02, 2013 10:40 pm, edited 1 time in total.
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Hi fourteenstix,
For the second question, you can set up a "Tic Tac Toe" Board (other companies and instructors might call it something else) to keep track of the information in the prompt. The key is to break the information down into "YES" vs "NOT YES (which is "NO" and "UNSURE" combined).
Notice the Grand Total (800 students) is in the lower-right box and the 200 who said "YES to JUST M" is the left column/middle box. The rest of the data can be transferred from the original table and/or calculated.
The answer to this question is the middle box.
GMAT assassins aren't born, they're made,
Rich
For the second question, you can set up a "Tic Tac Toe" Board (other companies and instructors might call it something else) to keep track of the information in the prompt. The key is to break the information down into "YES" vs "NOT YES (which is "NO" and "UNSURE" combined).
Notice the Grand Total (800 students) is in the lower-right box and the 200 who said "YES to JUST M" is the left column/middle box. The rest of the data can be transferred from the original table and/or calculated.
The answer to this question is the middle box.
GMAT assassins aren't born, they're made,
Rich
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Woah hold on there Rich![email protected] wrote:
Notice the Grand Total (800 students) is in the lower-right box and the 200 who said "YES to JUST M" is the left column/middle box. The rest of the data can be transferred from the original table and/or calculated.
The answer to this question is the middle box.
How do we tackle the unsure box in the question? How did you fill the RYES-MYES box as 300?
A little more detail would be appreciated.
A good question also deserves a Thanks.
Messenger Boy: The Thesselonian you're fighting... he's the biggest man i've ever seen. I wouldn't want to fight him.
Achilles: That's why no-one will remember your name.
Messenger Boy: The Thesselonian you're fighting... he's the biggest man i've ever seen. I wouldn't want to fight him.
Achilles: That's why no-one will remember your name.
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Hi faraz_jeddah,
Notice the wording of the question. The prompt mentions "Yes" for one piece of info and "Not Yes" for another. This is the "hint" that tells you to convert the data into two groups (instead of 3) per *letter*: 'Yes' and 'Not Yes' (which means 'No' and 'Not Sure' added together).
Try creating the table on your own: Yes for M, Not Yes for M, Total and then Yes for R and Not Yes for R, Total
You'll then be able to answer the question that's asked.
GMAT assassins aren't born, they're made,
Rich
Notice the wording of the question. The prompt mentions "Yes" for one piece of info and "Not Yes" for another. This is the "hint" that tells you to convert the data into two groups (instead of 3) per *letter*: 'Yes' and 'Not Yes' (which means 'No' and 'Not Sure' added together).
Try creating the table on your own: Yes for M, Not Yes for M, Total and then Yes for R and Not Yes for R, Total
You'll then be able to answer the question that's asked.
GMAT assassins aren't born, they're made,
Rich
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Two conditions that fulfill the multiple of 8 solution[email protected] wrote:Hi fourteenstix,
It's normally best to list just 1 question per post, but I'll answer both questions here:
First, the probability question. This question has LOTS of details that you have notice if you're going to answer it correctly. You'll notice that the answers have 8 as a common denominator (this provides an interesting hint to how the "math" will work. You should also notice that the question stem asks you to consider the numbers from 1 to 96, inclusive (and it's interesting that 96 is a multiple of 8...).
The prompt asks you to think about (n)(n+1)(n+2), so you'll be dealing with 3 consecutive integers multiplied together. For a number to be divisible by 8, it must include at least three 2's when the number is broken down using prime factorization:
For example: (1)(2)(3) = 6 which is NOT divisible by 8 (obviously), but you'll notice that there's just ONE 2.
For example: (2)(3)(4) = 24 which IS divisible by 8; you'll notice that there ARE THREE 2s (the 2 has one and the 4 has two).
So, we're looking for all the options that have three 2s in them...
Any option that is (even)(odd)(even) will include three 2s
Any option that has (odd)(multiple of 8)(odd) will also include three 2s
If you consider the first 8 possibilities
(1)(2)(3) = NO
(2)(3)(4) = YES
(3)(4)(5) = NO
(4)(5)(6) = YES
(5)(6)(7) = NO
(6)(7)(8) = YES
(7)(8)(9) = YES
(8)(9)(10) = YES
5/8 are what we're looking for. This pattern continues through every "set of 8", so the final answer is D
GMAT assassins aren't born, they're made,
Rich
n is even or n+1 is a multiple of 8
There are 48 Even Numbers and 12 multiples of 8 and hence 60/96 or 5/8 is the probability
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Second Que, differnt approach:
Let yes to neither = x
Given: If 200 students answered Yes only for M; and from table we know yes to M = 500, therefore, 500-200 = 300 students said Yes to M and R both
Also from table, 400 students said yes to R, therefore 400 - 300 = 100 students said yes to Only R
So from Formula:
Total = yes to M + Yes to R - Yes to both + yes to neither
800 = 500 + 400 - 300 + X
800 = 600 + x
therefore x = 200, ans
Let yes to neither = x
Given: If 200 students answered Yes only for M; and from table we know yes to M = 500, therefore, 500-200 = 300 students said Yes to M and R both
Also from table, 400 students said yes to R, therefore 400 - 300 = 100 students said yes to Only R
So from Formula:
Total = yes to M + Yes to R - Yes to both + yes to neither
800 = 500 + 400 - 300 + X
800 = 600 + x
therefore x = 200, ans
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I thought I'd point out that Rich's "Tic Tac Toe" Board approach is also known as the "group grid approach" or, the "Double Matrix method."
This technique can be used for most questions featuring a population in which each member has two characteristics associated with it.
Here, we have a population of students, and the two characteristics are:
- subject M interesting-yes, subject M interesting-not-yes
- subject R interesting-yes, subject R interesting-not-yes
To learn more about this technique, watch our free video: https://www.gmatprepnow.com/module/gmat- ... ems?id=919
Then try these additional practice questions that can be solved using the Double Matrix Method:
- https://www.beatthegmat.com/mba/2011/05/ ... question-1
- https://www.beatthegmat.com/mba/2011/05/ ... question-2
- https://www.beatthegmat.com/mba/2011/05/ ... question-3
- https://www.beatthegmat.com/ds-quest-t187706.html
- https://www.beatthegmat.com/overlapping- ... 83320.html
- https://www.beatthegmat.com/finance-majo ... 67425.html
- https://www.beatthegmat.com/ds-french-ja ... 22297.html
- https://www.beatthegmat.com/sets-t269449.html#692540
- https://www.beatthegmat.com/in-costume-f ... tml#692116
Cheers,
Brent
This technique can be used for most questions featuring a population in which each member has two characteristics associated with it.
Here, we have a population of students, and the two characteristics are:
- subject M interesting-yes, subject M interesting-not-yes
- subject R interesting-yes, subject R interesting-not-yes
To learn more about this technique, watch our free video: https://www.gmatprepnow.com/module/gmat- ... ems?id=919
Then try these additional practice questions that can be solved using the Double Matrix Method:
- https://www.beatthegmat.com/mba/2011/05/ ... question-1
- https://www.beatthegmat.com/mba/2011/05/ ... question-2
- https://www.beatthegmat.com/mba/2011/05/ ... question-3
- https://www.beatthegmat.com/ds-quest-t187706.html
- https://www.beatthegmat.com/overlapping- ... 83320.html
- https://www.beatthegmat.com/finance-majo ... 67425.html
- https://www.beatthegmat.com/ds-french-ja ... 22297.html
- https://www.beatthegmat.com/sets-t269449.html#692540
- https://www.beatthegmat.com/in-costume-f ... tml#692116
Cheers,
Brent