GMAT Data Sufficiency Discussions

I don't think I'm understanding the question right, could you explain your answer?

Thanks

My explanation would be something like this:

Question simply says that
1) Fran is standing on the ground
2) Fran jumps (ofcourse in the air) and lands back on the ground
3) Fran has spend some time in the air (going up and coming down)
4) If the total time spend (going up + coming down) is t seconds
5) Then the maximum height Fran can reach can be described in terms of will be 1.22 t^ 2

Actual Question
===============
If Fran makes a jump, has he spend total time (going up + coming down) less than 1 sec ?

Answer
======
This is a kind of yes/no question.
So according to 1) Fed has attained max height of 1 m.
Which means
1.22 t^2 = 1 i.e.
t^ 2 = 1/1.22 i.e.
t = (1/1.22) ^ 1/2

Which shows that we can answer the question that whether Fren has spend less than 1 second or not.
So 1 is sufficient.

According to 2) Fran has spend more than 1/4 of a second going up.
More than 1/4 can be 0.26 sec or 0.5 second or 1.4 second etc.
Also remember that Total time = time to go up + time to come down.
Also there is no way that we can know what is the time Fran ahs taken to come down.

This means 2 is not sufficient.

Hence, answer is (A).

Hope this helps.
My explanation would be something like this:

Question simply says that
1) Fran is standing on the ground
2) Fran jumps (ofcourse in the air) and lands back on the ground
3) Fran has spend some time in the air (going up and coming down)
4) If the total time spend (going up + coming down) is t seconds
5) Then the maximum height Fran can reach can be described in terms of will be 1.22 t^ 2

Actual Question
===============
If Fran makes a jump, has he spend total time (going up + coming down) less than 1 sec ?

Answer
======
This is a kind of yes/no question.
So according to 1) Fed has attained max height of 1 m.
Which means
1.22 t^2 = 1 i.e.
t^ 2 = 1/1.22 i.e.
t = (1/1.22) ^ 1/2

Which shows that we can answer the question that whether Fren has spend less than 1 second or not.
So 1 is sufficient.

According to 2) Fran has spend more than 1/4 of a second going up.
More than 1/4 can be 0.26 sec or 0.5 second or 1.4 second etc.
Also remember that Total time = time to go up + time to come down.
Also there is no way that we can know what is the time Fran ahs taken to come down.

This means 2 is not sufficient.

Hence, answer is (A).

Hope this helps.


Totally makes sense, I was making a very careless mistake ...

Can somebody please help in the following question. Also it would be really helpful in you can provide completion explanation of the answer as i know the answer but don't know how to solve it. Also guidance how it can be solved during exam in 2/3 mins.
if x,y,z are integers and xy + z is an odd integer, is x an even integer?
1) xy + xz is an even integer
2) y + xz is an odd integer

Thanks in advance

Is there a place i can get similar questions?

Can somebody please help in the following question. Also it would be really helpful in you can provide completion explanation of the answer as i know the answer but don't know how to solve it. Also guidance how it can be solved during exam in 2/3 mins.
if x,y,z are integers and xy + z is an odd integer, is x an even integer?
1) xy + xz is an even integer
2) y + xz is an odd integer

Thanks in advance


xy+z is odd
so,either xy is odd or z is odd.if x is even,z is odd and if x is odd,z can be odd or even depending on y.

statement 1:
xy+xz is even
even-odd=odd
xy+xz-xy-z=odd
z(x-1)=odd
x-1=odd
x=even
sufficient.

statement 2:
y+xz is odd
odd+odd=even
xy+z+y+xz=even
(x+1)(y+z)=even
three possibilities.both even OR one even,other odd
not sufficient.

option (A)
=>statement 1 is sufficient.

hope that helps.

Hi

Can anybody help me with these

1)If the units digit of the three-digit positive integer k is nonzero, what is the tens digit of k?
(1) The tens digit of k + 9 is 3.
(2) The tens digit of k + 4 is 2.

2)If 2 different representatives are to be selected at random from a group of 10 employees and if p is the probability that both representatives selected will be women, is p > 1/2 ?
(1) More than 1/2 of the 10 employees are women.
(2) The probability that both representatives selected will be men is less than 1/10

Hi

Can anybody help me with these

1)If the units digit of the three-digit positive integer k is nonzero, what is the tens digit of k?
(1) The tens digit of k + 9 is 3.
(2) The tens digit of k + 4 is 2.

Assume units digit of k is u and tens digit is t.

Solving using (1)
u can be one of following 1,2,3,4,5,6,7,8,9
Adding 9 to u will always give 1 as carry over (irrespective of value of u, try adding 1+ 9, 2+9....9+9).
So, 1 (carry over ) + t = 3 (as given by statement (1)).
Which means t can only be 2. So (1) is sufficient.

Solving using (2), in a similar manner
u can be one of following 1,2,3,4,5,6,7,8,9
Adding 4 to u, can give following as carry over:
0 (if u is either 1 or 2 or 3 or 4 or 5)
1 (if u is either 6 or 7 or 8 or 9)

So with 0 as carry over 0 + t = 2 ===> t = 2
with 1 as carry over 1 + t = 2 ===> t = 1.
Which means statement (2) is not sufficient.

Hence answer is (A).


2)If 2 different representatives are to be selected at random from a group of 10 employees and if p is the probability that both representatives selected will be women, is p > 1/2 ?
(1) More than 1/2 of the 10 employees are women.
(2) The probability that both representatives selected will be men is less than 1/10

Solving using (1)
Women can be 6 or 7 or 8 or 9 or 10.
i.e. probability p can be
(6/10 * 5/9), which is OR
(7/10 * 6/9), which is OR
(8/10 * 7/9), which is > 1/2

So (1) is not sufficient.

Solving using (2)
Suppose men are 4, which means probability of selecting both men is (4/10 * 3/9), which is > 1/10. Hence men cannot be 4.

Suppose men are 3, which means probability of selecting both men is (3/10 * 2/9), which is If men can be maximum 3 means women can be minimum 7.
So with 7 women we have already seen the probability will be (7/10 * 6/9), which is but with 8 women probability will be (8/10 * 7/9), which is > 1/2.

hence (2) is also not sufficient.

Solving using (1) and (2)
We have already seen that
(1) implies Women can be 6 or 7 or 8 or 9 or 10.
(2) implies Women can be 7 or 8 or 9 or 10.

combining (1) and (2) implies Women can be 7 or 8 or 9 or 10.
With seven selecting two women, probability is (7/10 * 6/9), which is With eight selecting two women, probability is (8/10 * 7/9), which is > 1/2.

Hence (1) & (2) together are not sufficient. So answer should be (E).


Hope that helps? What are the OA?

Thanks a lot rajatmeh! the OA's are A and E resp....

Here are a few i need help with,

A)
A box contains 10 light bulbs, fewer than half of which are defective. Two bulbs are to be drawn simultaneously from the box. If n of the bulbs in box are defective, what is the value of n?
(1)The probability that the two bulbs to be drawn will be defective is 1/15.
(2) The probability that one of the bulbs to be drawn will be defective and the other will not be defective is 7/15.

B)M = {-6, -5, -4, -3, -2}
T = {-2, -1, 0, 1, 2, 3}
If an integer is to be randomly selected from set M above and an integer is to be randomly selected from set T above, what is the probability that the product of the two integers will be negative?

A.0
B.1/3
C.2/5
D.1/2
E.3/5


C)A certain company that sells only cars and trucks reported that revenues from car sales in 1997 were down 11 percent from 1996 and revenues from truck sales in 1997 were up 7 percent from 1996. If total revenues from car sales and truck sales in 1997 were up 1 percent from 1996, what is the ratio of revenue from car sales in 1996 to revenue from truck sales in 1996?

A.1 : 2
B.4 : 5
C.1 : 1
D.3 : 2
E.5 : 3

Here are a few i need help with,

A)
A box contains 10 light bulbs, fewer than half of which are defective. Two bulbs are to be drawn simultaneously from the box. If n of the bulbs in box are defective, what is the value of n?
(1) The probability that the two bulbs to be drawn will be defective is 1/15.
(2) The probability that one of the bulbs to be drawn will be defective and the other will not be defective is 7/15.

B)M = {-6, -5, -4, -3, -2}
T = {-2, -1, 0, 1, 2, 3}
If an integer is to be randomly selected from set M above and an integer is to be randomly selected from set T above, what is the probability that the product of the two integers will be negative?

A. 0
B. 1/3
C. 2/5
D. 1/2
E. 3/5


C)A certain company that sells only cars and trucks reported that revenues from car sales in 1997 were down 11 percent from 1996 and revenues from truck sales in 1997 were up 7 percent from 1996. If total revenues from car sales and truck sales in 1997 were up 1 percent from 1996, what is the ratio of revenue from car sales in 1996 to revenue from truck sales in 1996?

A. 1 : 2
B. 4 : 5
C. 1 : 1
D. 3 : 2
E. 5 : 3


A)
A box contains 10 light bulbs, fewer than half of which are defective. Two bulbs are to be drawn simultaneously from the box. If n of the bulbs in box are defective, what is the value of n?
(1) The probability that the two bulbs to be drawn will be defective is 1/15.
(2) The probability that one of the bulbs to be drawn will be defectiv

(1) The probability that the two bulbs to be drawn will be defective is 1/15.
==> n/10 * (n-1)/9 = 1/15 ==> n=3
(2) The probability that one of the bulbs to be drawn will be defective and the other will not be defective is 7/15.
(10-n)/10 * n/9 * 2 = 7/15 ==> n=3



2) The probability that one of the bulbs to be drawn will be defective and the other will not be defective is 7/15.

B)M = {-6, -5, -4, -3, -2}
T = {-2, -1, 0, 1, 2, 3}
If an integer is to be randomly selected from set M above and an integer is to be randomly selected from set T above, what is the probability that the product of the two integers will be negative?


total possibility=30

in 15 case product negative

so ans is 1/2



C)A certain company that sells only cars and trucks reported that revenues from car sales in 1997 were down 11 percent from 1996 and revenues from truck sales in 1997 were up 7 percent from 1996. If total revenues from car sales and truck sales in 1997 were up 1 percent from 1996, what is the ratio of revenue from car sales in 1996 to revenue from truck sales in 1996?

A. 1 : 2
B. 4 : 5
C. 1 : 1
D. 3 : 2
E. 5 : 3

in 1996 car revenue =x and truck =y


then in 1997 for car=0.89x and truck=1.07y


now (0.89x+1.07y)/(x+y)=1.01


after solving u will get 6/12=1/2 ans =option 1

nice post !!!:cheers:

If in a DS questions (1) and (2) both are sufficient to answer the question, but the answer is not consistent. What will be the answer choice?

(D) or (E)

E.g. if question asks that if x >y?

Solving statement (1) we get xy

Will the answer be (D) --Both statements are sufficient OR
Will the answer be (E) --Both statements together are not sufficient

Experts please reply.

Hi Rajat
In the case above, the answer will be E.

However, if let us say you have a question that asks you what is the value of X, Y, Z etc
Statement 1 gives you 10
Statement 2 gives you 30

Your answer option will be D. It doesn't matter what the value of the variable is. As long as the statement gives you a definite value, it is sufficient.

But why is that so?

Even in the example I have provided, you are getting a definite answer, though different in case of both the statements.
In your example also, you are getting a definite answer, though different in case of both the statements.

My question is
"Does in DS questions if statements (1) and (2) both are independently able to answer the question, then
If both the statements give different answers (irrespective of answer type "yes/no" or may be "10/30" etc). In such case do we choose option "D" or option "E".

hey ...can someone help me with these

1)
What is the sum of a certain pair of consecutive odd integers?
(1) At least one of the integers is negative.
(2) At least one of the integers is positive.


2)If x is a positive integer, is the remainder 0 when 3x + 1 is divided by 10?
(1) x = 4n + 2, where n is a positive integer.
(2) x > 4

in the 2nd question above...the expression is 3^x + 1

Lets solve the 2nd question.

Is 3^x + 1 divisible by 10?

For these type of questions its always better to write the first 4-5 terms. Then we can solve even if we do not know any formulas.

If you observe, 3^0 = 1; 3^1 = 3; 3^2 = 9; 3^3 = 27; 3^4 = 81; so the last digit always repeats after every four terms. So, we have a generalization.

So, consider option 1; x=4n+2; where n is a +ve integer; gives x = 2, 6, 10 ...and so on.

The last digitin all these numbers is 9.

So 3^x + 1 has last digit of 0; hence divisible by 10.

2. x>4, xould be anything....

So, the answer is A. (can be solved with option 1 alone).


Cheers,
Adarsh.


Hi
I will help you with the first problem.
The correct answer is C.

1 - At least one of them is negative - Not sufficient as there are multiple possibilities
2 - At least one of them is positive - Not sufficient as there are multiple possibilities.

However, if you combine the 2, the only possibility is -1 and 1. Together, you can answer the question and hence the answer is C.

For the other problem, suggest that you study the properties of powers of 3. What happens when you have even powers of 3 like 3^2, 3^4 so on and so forth. You can derive the answer.

(And by the way, both the problems are given in Kaplan ;))

hey ...can someone help me with these

1)
What is the sum of a certain pair of consecutive odd integers?
(1) At least one of the integers is negative.
(2) At least one of the integers is positive.


2)If x is a positive integer, is the remainder 0 when 3x + 1 is divided by 10?
(1) x = 4n + 2, where n is a positive integer.
(2) x > 4

Hi Puys,

Have a co-ordinate geometry question.

Q: Straight lines l & k intersect at point (4,3) on the xy plane. Is the product of slopes of these lines negative?

1. The product of x-intercepts of the lines is positive.
2. The product of y-intercepts of the lines is negative.


Regards,
Adarsh.

Ans is C .
lets the equation is x/a + y/b = 1 .
so , slope is = -b/a
for first line slope = -b1/a1
for second line = -b2/a2
now product of slope = b1*b2/ a1*a2
now b1*b2 = +ve and a1*a2= -ve
so product of slope = -ve .

for the second case u forgot to mention values of m and p as 6 and 10. which have LCM of 30 but remainder is not 1 so second statement can not alone find out whether r>1 or not.
I guess answer be C caz it gives m and p as 6 and 10 respectively making remainder r =4.

Is it D?
According to first statement and given data if m=n then p is also even and n+2=According to sec statement LCM of m and p is 30. Factors of 30 are 1, 2, 3, 5, 6, 10, 15, 30. m>2 So possible values of m and p are 3 and 10 or 5 and 6 and in both the cases remainder is 1.
So both statements are individually sufficient.




please explain 1st reasoning more elaborately its not clear.I think answer should be C.