GMAT Data Sufficiency Discussions

MBA GMAT
1661
plz explain this to me.

Is the positive integer N a perfect square?

(1) The number of distinct factors of N is even.
(2) The sum of all distinct factors of N is even.


I am not sure.. but i think it must be option D
Golden rule
1. A perfect number always has odd number of factors whose sum is odd

2. A perfect number always has odd number of odd factors and even number of even factors
1662

Nutty..your answer should be correct..
Adding third rule
I am not sure.. but i think it must be option D
Golden rule
1. A perfect number always has odd number of factors whose sum is odd

2. A perfect number always has odd number of odd factors and even number of even factors

3.For a perfect square number,sum of its factors is always odd.
1663

Nutty..your answer should be correct..
Adding third rule


@pj02:
isnt the 3rd rule re-iteration of the 1st one itself..??..

can someone plz share the OA..??..
1664
@pj02:
"isnt the 3rd rule re-iteration of the 1st one itself..??.. "

can someone plz share the OA..??..



"isnt the 3rd rule re-iteration of the 1st one itself..??.. "

Hi Hi Hi Hi....

Both of the rule ARE SUFFICIENT....:-)
1665
If Ann saves x dollars each week and Beth saves y dollars each week, what is the total amount that they save per week?
(1) Beth saves $5 more per week than Ann saves per week.
(2) It takes Ann 6 weeks to save the same amount that Beth saves in 5 weeks.
1666
If Ann saves x dollars each week and Beth saves y dollars each week, what is the total amount that they save per week?
(1) Beth saves $5 more per week than Ann saves per week.
(2) It takes Ann 6 weeks to save the same amount that Beth saves in 5 weeks.


Ann savings/week = x
B's savings/week = y

we have to find the value of x+y?

Statement 1:
==========
y= x+5. Nt suff

Statement 2:
==========
B = y (savings/week)

A = 5y/6 (savings/week)

So total savings = 11y/6 .Nt suff

Combining both the statements:

y-5y/6 = 5 .so y=30 and x =25.so total savings/week = 55.

so, both the statements are suff to solve the q
1667
If Ann saves
x dollars each week and Beth saves y dollars each week, what is the total amount that they save per week?
(1) Beth saves $5 more per week than Ann saves per week.
(2) It takes Ann 6 weeks to save the same amount that Beth saves in 5 weeks.


B = A+5---(1)
so total = 2A+5=>...Not sufficient

6A = 5B....(2)=> not sufficient

together..C)
1668

thanks.. I believe I misunderstood the questions.. that really helped!! ;)

Ann savings/week = x
B's savings/week = y

we have to find the value of x+y?

Statement 1:
==========
y= x+5. Nt suff

Statement 2:
==========
B = y (savings/week)

A = 5y/6 (savings/week)

So total savings = 11y/6 .Nt suff

Combining both the statements:

y-5y/6 = 5 .so y=30 and x =25.so total savings/week = 55.

so, both the statements are suff to solve the q

B = A+5---(1)
so total = 2A+5=>...Not sufficient

6A = 5B....(2)=> not sufficient

together..C)
1669

plz explain option 1) how is this inequality sufficient???

Is x y > r s?
(1) x > r and y s
(2) y = 2, s = 3, r = 5, and x = 6.
1670
exemba Says
plz explain option 1) how is this inequality sufficient???



Assume x = r
Now, from 1 we have y Now, lets say y =3, and s = 4

x-y will be x-3
r-s will be x-4

You surely can therefore say that, x - 3 > x - 4

All the above explanation is good for a value of r thats equal to x.
If r is less than x, then even better...no matter what the RHS can never be more than the LHS.

Hence sufficient.
1671
exemba Says
plz explain option 1) how is this inequality sufficient???



Here u can rewrite the inequality as x+s>r+y

so from 1) x>r and s>y so we can say that x+s> r+y

I hope this helps.
1672
If Ann saves
x dollars each week and Beth saves y dollars each week, what is the total amount that they save per week?
(1) Beth saves $5 more per week than Ann saves per week.

(2) It takes Ann 6 weeks to save the same amount that Beth saves in 5 weeks.


IMO C

from 1) we have

x+5=y In suff

from 2 we have 6(x+5)= 5y Insuff

combining 1) and 2) we have 2 unknowns and 2 eqs

So C.


1673
Here u can rewrite the inequality as x+s>r+y

so from 1) x>r and s>y so we can say that x+s> r+y

I hope this helps.


this is the right approach
1674
What is the ratio of the average (arithmetic mean) height of students in class X to the average height of students in class Y?
(1) The average height of the students in class X is 120 centimeters.
(2) The average height of the students in class X and class Y combined is 126 centimeters.
1675
If x(x - 5)(x + 2) = 0, is x negative?

(1) x2 7x 0

(2) x2 2x 15 0
PS: x2 = x^2 ;)
1676
Of the students in a certain school, 15 percent are enrolled in an art class and 10 percent are enrolled in a music class. What percent of the students in the school are enrolled in neither an art class nor a music class?

(1) 2/3 of the students who are enrolled in an art class are also enrolled in a music class.
(2) There are more than 100 students in the school.
1677
What is the ratio of the average (arithmetic mean) height of students in class
X to the average height of students in class Y?
(1) The average height of the students in class X is 120 centimeters.
(2) The average height of the students in class X and class Y combined is 126 centimeters.

let the number of students be x and y and respective heights are p,q
we have to find out-p/x/q/y=py/qx
stat1.p=120x
stat2.p+q=126x+126y
none of the statement give a unique answer,so E
1678
If x(x - 5)(x + 2) = 0, is x negative?


(1) x2 7x 0

(2) x2 2x 15 0
PS: x2 = x^2 ;)


from question ,x is either-0,5,-2
stat1.x=0,7...suffecient
stat2.x=5,3...suff
So answer is D
1679
Of the students in a certain school, 15 percent are enrolled in an art class and 10 percent are enrolled in a music class. What percent of the students in the school are enrolled in neither an art class nor a music class?


(1) 2/3 of the students who are enrolled in an art class are also enrolled in a music class.
(2) There are more than 100 students in the school.


i thnk the answer will be A.
neither in arts or music=100-15-10-200/3
1680
What is the ratio of the average (arithmetic mean) height of students in class X to the average height of students in class Y?
(1) The average height of the students in class X is 120 centimeters.
(2) The average height of the students in class X and class Y combined is 126 centimeters.



Statement 1:
==========
Avg of x = 120..Nt suff to ans the q

Statement 2:
==========
Total sum of (x+y) / Total no.of students in x & y = 126.Nt suff

Combining both cannot also give the exact amount.
So my take for the above q is option E