Is the sum of all the numbers between

Q) Is the sum of all the numbers between prime numbers x and y an even or an odd number?

1)    x = 3  y = 31
2)    y is the largest two digit number, x is even

A. Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient.
B. Statement (2) ALONE is sufficient, but statement (1) alone is not sufficient.
C. BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient.
D. EACH statement ALONE is sufficient.
E. Statements (1) and (2) TOGETHER are NOT sufficient.


To answer data sufficiency questions you don’t have to solve the problem. You just have to find the sufficient condition to prove the answer choice.

Question:  sum(x+1, x+2….y-1) = Odd or Even

Condition 1: x = 3  y = 31

Sum (4, 5,….30) = odd or Even

You don’t have to solve this but since you are aware of the sequence of numbers between x and y, the answer can be found.

Condition 1 is enough to answer the question

Condition 2: y is the largest two-digit number, x is even

The question mentions that x and y are prime numbers. Condition 2 provides two more additional information about the prime numbers.

Y is the largest two-digit number

Largest two-digit number is 99 but since question specifies that y is a prime number, y should be largest two digit prime number.

The only even prime number is 2. So x =2

Therefore we have to find the sum of all the numbers between  x = 2 and y= largest two digit prime number

Note: One mistake that test takers make is to spend time to find y, which is not necessary.
Once we get x and y, the sum can be calculated based on Arithmetic Progression.

Correct Answer: D

Essential GMAT Reading Comprehension Guide

After you read F1GMAT’s Essential GMAT Reading Comprehension Guide, you will:

1. Complete GMAT RC Questions in less than 1 minute and 50 seconds

2. Read Faster

3. Take Notes Effectively

4. Collect and Interpret Facts

5. Speed up Summary Creation

6. Remember Information

7. Question the Author   

8. Learn to answer GMAT Reading Comprehension Title question   

9. Learn to Solve GMAT Reading Comprehension Main Idea Question   

10.Learn to Solve GMAT Reading comprehension inference question   

11. Learn to Solve GMAT Reading Comprehension Detail Questions   

12. Learn to Organize passage in GMAT Reading Comprehension   

13. Learn to Identify style/tone or attitude of the author

14. Learn to Improve GMAT Reading Comprehension Score

Download Essential GMAT Reading Comprehension Guide

Mastering GMAT Critical Reasoning

After you read F1GMAT’s Mastering GMAT Critical Reasoning Guide, you will:

1) Learn to eliminate out of scope answer choices

2) Learn to spot logical fallacies

3) Learn to read questions by focusing on the holy trinity – premise, assumption, and conclusion.

4) Learn to disregard filler information

5) Complete GMAT CR Questions in less than 1 minute and 40 seconds

Download Mastering GMAT Critical Reasoning

Get F1GMAT's Newsletters (Best in the Industry)
Included in the Newsletter:

  • Ranking Analysis
  • Post-MBA Salary Trends
  • Post-MBA Job Function & Industry Analysis
  • Post-MBA City Review
  • MBA Application Essay Tips
  • School Specific Essay Tips
  • GMAT Preparation Tips
  • MBA Admission Interview Tips
  • School Specific Interview Tips
  • Funding Guidance and
  • Special Consultation Service (only for Subscribers)

Subscribe to F1GMAT's Newsletter