Hello everyone,

I have been studying for the GMAT for a few months. My GMAT exam date is on 25th of August, 2015. From the very beginning, I had major issues with DS questions. I have improved over the last few weeks but they still remain a hurdle towards a good final grade.

My last CAT from GMATPrep was as follows:
650 Q43 (61%) V37 (81%)
The problem is that of the 18 wrong questions in Quant, 9 of them were DS questions and not necessarily of high level. More specifically, these were the DS questions I got wrong:
What would your advice be towards improving on DS questions?

1)If x and y are integers greater than 1, is x a multiple of y?

(1) 3y^2+7y=x
(2) x^2-x is a multiple of y


2)A contractor combined x tons of a gravel mixture that contained 10 percent gravel G, by weight, with y tons of a mixture that contained 2 percent gravel G, by weight, to produce z tons of a mixture that was 5 percent gravel G, by weight. What is the value of x ?

(1) y = 10

(2) z = 16


3)In the figure shown, what is the value of x?


(1) The length of line segment QR is equal to the length of line segment RS

(2) The length of line segment ST is equal to the length of line segment TU


4)Janson's salary and Karen's salary were each p percent greater in 1998 than in 1995. What is the value of p?

(1) In 1995 Karen's salary was $2,000 greater than Jason's.
(2) In 1998 Karen's salary was $2,440 greater than Jason's.


5)If s and t are two different numbers on the number line, is s + t = 0 ?

(1) Distance between s and 0 is the same as distance between t and 0
(2) 0 is between s and t

6)If it took Carlos 1/2 hour to cycle from his house to the library yesterday, was the distance that he cycled greater than 6 miles? (Note: 1 mile=5280 feet.

1) The average speed at which Carlos cycled from his house to the library yesterday was greater than 16 feet per second.
2) The average speed at which Carlos cycled from his house to the library yesterday was greater than 18 feet per second.

7)For the students in class A, the range of their heights is r centimeters and the greatest height is g centimeters. For the students in class B, the range of their heights is s centimeters and the greatest height is h centimeters. Is the least height of the students in class A greater than the least height of the students in class B ?

(1) r < s
(2) g > h

8)Is x less than 20?

(1) The sum of x and y is less than 20.
(2) y is less than 20.

9)If the average (arithmetic mean) of four different numbers is 30, how many of the numbers are greater than 30?

(1) None of the four numbers is greater than 60.
(2) Two of the four numbers are 9 and 10, respectively.