DS on saturday and sunday

As usual here is the list of questions that made me to have a second look.

1. Is x2 equal to xy?
(1) x2 - y2 = (x + 5)(y - 5)
(2) x = y

I answered it D but the answer given is B.

Option 2 is sufficient as it says x = y which means that x2 equal to xy.
So, A & E are eliminated.
Lets see the option 1.
x2 - y2 = xy + 5y - 5x - 25
x2 = y2 + xy + 5y - 5x - 25
x2 = xy + some value (y2 + 5y - 5x - 25)
So, i came to a conclusion that x2 not equal to xy. What i missed is when y = 0 and x = -5, x2

equal to xy.
So, option 1 is insufficient.


2. At a certain university, if 50 percent of the people who inquire about admission policies

actually submit applications for admission, what percent of those who submit applications for

admission enroll in classes at the university?
(1) Fifteen percent of those who submit applications for admission are accepted at the

university.
(2) Eighty percent of those who are accepted send a deposit to the university.

This sort of questions confuse me. Sometimes we shud assume that when a university has accepted

an application then it means the student has enrolled. Sometimes u don't.

3. A jewelry dealer initially offered a bracelet for sale at an asking price that would give a

profit to the dealer of 40 percent of the original cost. What was the original cost of the

bracelet?
(1) After reducing this asking price by 10 percent, the jewelry dealer sold the bracelet at a

profit of $403.
(2) The jewelry dealer sold the bracelet for $1,953.

I answered D and the actual answer is A.
I didn't understand why option 2 is not sufficient. Is it because the asking price is different

from the selling price?

4. The surface area of a square tabletop was changed so that one of the dimensions was reduced by

1 inch and the other dimension was increased by 2 inches. What was the surface area before these

changes were made?
(1) After the changes were made, the surface area was 70 square inches.
(2) There was a 25 percent increase in one of the dimensions.
I answered C and the actual answer is D.
I didn't understand how?


5. If ? denotes a mathematical operation, does
x?y=y?x for all x and y?
(1) For all x and y, x?y = 2(x2 + y2).
(2) For all y, 0?y = 2 y2
I answered D and the actual answer is A.
I didn't understand how? Based on option 2, we can say that x?y not equal to y?x for all x and y.

isn't it?


6. If b is the product of three consecutive positive integers c, c + 1, and c + 2, is b a

multiple of 24 ?
(1) b is a multiple of 3,
(2) c is odd.
I answered E and the actual answer is A.
I didn't understand how?
if c = 1, b = 1*2*3 which is not divisible by 24.
if c = 6, b = 6*7*8 which is divisible by 24.
if c = 6, b = 15*16*17 which is divisible by 24.


7. Is the integer n a multiple of 140 ?
(1) n is a multiple of 10.
(2) n is a multiple of 14.
I answered C and the actual answer is E.
I didn't understand how?

Areas to improve.
1. Not reading the question stem properly.
2. Though i know the correct answer i mark it wrongly.
3. Concentration shud improve.

There were some 12 DS sets of questions each containing 25 questions to be answered within 30

minutes. Most of the time i took less than 25 minutes. Whenever i took a long break (indicated

here by a line break :)) i scored less and took longer minutes to complete.

Correct/Wrong

19/6
20/5
22/3
19/6

18/7
20/5

23/2

23/2

19/6
20/5