GMAT Problem Solving Discussions

MBA
783
450y=n^3
450y=(y/x)^3
450=y^2/x^3
3^2*5^2*2*x^3=y^2
that means 2*x^3 must be perfect square
None satisfy these condition so answer is none

" 3^2*5^2*2*x^3=y^2
that means 2*x^3 must be perfect square
None satisfy these condition so answer is none"

If I take x=2*2*2, then 3^2*5^2*2*x^3=y^2 stands valid.
so y here becomes 3*5*2*2

P.S. This is a public forum. Even if you feel the answer someone has posted is wrong, no need to groan 😃 I hope eric.segal1 agrees 😃
784
if n and y are positive integers such that 450y = n^3
which of the following must be an integer

1 y/(3 *2*2*5)
2 y/(3*3*2*5)
3 y/(3*2*5*5)

a none
b 1 only
c 2 only
d 3 only
e 1 2 and 3

if you doesn't understand what i told i will explain in words
let n be equal to y/x
now
450y=y^3/x^3
canceling y
450x^3=y^2
now 450x^3 has to perfect square
9^2 and 5^2 are factors in 450 that are perfect square
now 2*x^3 has to perfect square That means there has to an odd power of 2 in x and all others has to be even powers
1 has both conditions wrong
2 has 3^2,2 but 5 has even power
3 has 3 having odd power and 2 with even power
So none of them can be correct.

You can groan if you feel this is useful and thank if you feel this is useful as you told this is a public forum.
785

thats the rite answer, NONE
thanks for the elaborate explanation

786
if you doesn't understand what i told i will explain in words
let n be equal to y/x
now
450y=y^3/x^3
canceling y
450x^3=y^2
now 450x^3 has to perfect square
9^2 and 5^2 are factors in 450 that are perfect square
now 2*x^3 has to perfect square That means there has to an odd power of 2 in x and all others has to be even powers
1 has both conditions wrong
2 has 3^2,2 but 5 has even power
3 has 3 having odd power and 2 with even power
So none of them can be correct.

You can groan if you feel this is useful and thank if you feel this is useful as you told this is a public forum.

i guess vicky verma has pointed at yr doubt precisly and i think u understand where was te flaw in yr answer afterall.
now guys throw up the nxt one and lets make this a bit more challenging.

and i think groans r not a problem, its wat its meant to be. Now throw the ext one in. we r all waiting.
787

The answer should be E

788
sats123 Says
The answer should be E

dude!!!

what question are you answering to 😃 and what's the explanation for your answer choice.
789

hey guys,

stuck on the following ques.. explanation would be nice.

the ques invloves solving numbers with underroots so please check image attached.

choices are
(1) 8 + 3underoot7
(2) 4 + 3underoot7
(3) 8
(4) 4
(5) underroot7

thanks....

790
hey guys,

stuck on the following ques.. explanation would be nice.

the ques invloves solving numbers with underroots so please check image attached.

choices are
(1) 8 + 3underoot7
(2) 4 + 3underoot7
(3) 8
(4) 4
(5) underroot7

thanks....


Lets approximate the whole thing ~= or less than root of 18.25
now =4+
Now from choices we can find the answer.
791
hey guys,

stuck on the following ques.. explanation would be nice.

the ques invloves solving numbers with underroots so please check image attached.

choices are
(1) 8 + 3underoot7
(2) 4 + 3underoot7
(3) 8
(4) 4
(5) underroot7

thanks....


Given number = sqrt[ 9sq.rt(7)+ 0.25 ]

For rough estimation eliminate 0.25 = approx 3 * 7^1/4 = approx 3* sq.rt(2.6) = approx 3 * (1.6) = approx 4.8

so (4) 4 should be the closest answer. Others are way beyond the number.

Neo
792
if n and y are positive integers such that 450y = n^3
which of the following must be an integer

1 y/(3 *2*2*5)
2 y/(3*3*2*5)
3 y/(3*2*5*5)

a none
b 1 only
c 2 only
d 3 only
e 1 2 and 3

The answer must be B

450y = n^3

=> 2*3^2*5^2* y = n^3

since n, y are +ve integers, y must be of the form 2^(3k-1) * 3^(3k-2)*5^(3k-2) where K=1,2,3...

We can give values to k and all of 1), 2), 3) will be satisfied. All we need is a integer when smth divides y. Isnt it?

For eg

When k=1 , y=2^2*3*5 => 1) gives 1, an integer. so holds true

When k=2, y=2^5*3^4*5^4 => 1),2),3) will be valid here. They all give integer.

So we see that 1) holds true for any value of k E N.

The qn asked refers to a choice which holds true i.e which is an integer for every value of k..

Hence B should be the choice..

Discussions if any are welcome..

Neo
793
if you doesn't understand what i told i will explain in words
let n be equal to y/x
now
450y=y^3/x^3
canceling y
450x^3=y^2
now 450x^3 has to perfect square
9^2 and 5^2 are factors in 450 that are perfect square
now 2*x^3 has to perfect square That means there has to an odd power of 2 in x and all others has to be even powers
1 has both conditions wrong
2 has 3^2,2 but 5 has even power
3 has 3 having odd power and 2 with even power
So none of them can be correct.

You can groan if you feel this is useful and thank if you feel this is useful as you told this is a public forum.


dude..i think you got it all wrong.. plz b patient to read my reasoning..

Firstly you assumed y=nx ; and proceeded with the problem. Fine as long as you dont forget your assumption.

and finally you have arrived at some possible notation of x. i.e odd and even powers of some numbers..fine with it too..

BUT the qn simply asks you if y is divided with some numbers then the result, would it be an integer or not?

How did you conclude that these some numbers given in the options should conform to the notation of x ?? It need not be.

Afterall the result from the options should be a integer and not n .

You have assumed that each option should inturn give you n:|. which is not true.

Is it clear? Revert back if any difficulties.

Neo
794

Great way to answer a question.
Answer with the analysis method followed.
I had understood that was wrong just didn't post because i wanted to stop that reply sequence.
I was also thinking this type of answer but got wrong
Thanks for the post.

The answer must be B

450y = n^3

=> 2*3^2*5^2* y = n^3

since n, y are +ve integers, y must be of the form 2^(3k-1) * 3^(3k-2)*5^(3k-2) where K=1,2,3...

We can give values to k and all of 1), 2), 3) will be satisfied. All we need is a integer when smth divides y. Isnt it?

For eg

When k=1 , y=2^2*3*5 => 1) gives 1, an integer. so holds true

When k=2, y=2^5*3^4*5^4 => 1),2),3) will be valid here. They all give integer.

So we see that 1) holds true for any value of k E N.

The qn asked refers to a choice which holds true i.e which is an integer for every value of k..

Hence B should be the choice..

Discussions if any are welcome..

Neo
795
Great way to answer a question.
Answer with the analysis method followed.
I had understood that was wrong just didn't post because i wanted to stop that reply sequence.
I was also thinking this type of answer but got wrong
Thanks for the post.


dude..its not a big deal if we post some wrong answers but when you know smth is wrong with your solution, don't refrain from posting the right one, lest someone else may take your wrong solution for granted. :wink:

That is why, we have the edit option to correct our posts.

and remember..No one will question your insanity here..All are pagal anyway..

anyways..Hoping for more qns and discussions from your side..

Cheers
Neo
796

1. A rectangular tiled floor consists of 70 square tiles. The rectangular floor is being rearranged so that 2 tiles will be removed from each row of tiles and 4 more rows of tiles will be added. After the change in layout, the floor will still have 70 tiles, and it will still be a rectangle. How many rows were in the tile floor before the change in layout?

A) 4

B) 7

C) 10

D) 14

E) 28

797

2. A club has 8 male and 8 female members. The club is choosing a committee of 6 members. The committee must have 3 male and 3 female members. How many different committees can be chosen?

A) 112,896

B) 3,136

C) 720

D) 112

E) 18

798
1. A rectangular tiled floor consists of 70 square tiles. The rectangular floor is being rearranged so that 2 tiles will be removed from each row of tiles and 4 more rows of tiles will be added. After the change in layout, the floor will still have 70 tiles, and it will still be a rectangle. How many rows were in the tile floor before the change in layout?

A) 4

B) 7

C) 10

D) 14

E) 28


L- Length of rectangle
B- breadth
S- side of square

Given L* B = 70*S^2 => (L/S)*(B/S) = 70=7 * 10

After change=> (L/S-2)*(B/S+4) = 70 = 7*10

Looking at the two eqns the obvious soln is

L/S=7 and B/S=10

Number of rows before change = B/S =10

Neo
799
2. A club has 8 male and 8 female members. The club is choosing a committee of 6 members. The committee must have 3 male and 3 female members. How many different committees can be chosen?

A) 112,896

B) 3,136

C) 720

D) 112

E) 18


8C3 * 8C3

Neo
800

Wrote GMATPrep test 2 yesterday. Scored 680 (QA:49 VA:38 ). Here are a few QA questions that barred me from getting a 50 in QA :-)


I was actually happy to see all these questions in my test. They seemed to be from moderate/high difficulty level. So I was sure of a good score in QA 😃

801
Wrote GMATPrep test 2 yesterday. Scored 680 (QA:49 VA:38 ). Here are a few QA questions that barred me from getting a 50 in QA :-)


I was actually happy to see all these questions in my test. They seemed to be from moderate/high difficulty level. So I was sure of a good score in QA :-)


To all the DS qns the ans is 3). Both statements are sufficient but neither alone.

and for the last one ans is 4) i.e 21/40

Keep posting
Neo
802
To all the DS qns the ans is 3). Both statements are sufficient but neither alone.

and for the last one ans is 4) i.e 21/40

Keep posting
Neo

Explainations ?? 😃