GMAT Prep From Platinum GMAT

GMAT Prep Materials

GMAT Practice Questions

Problem Solving · Data Sufficiency · Sentence Correction · Reading Comprehension · Critical Reasoning

GMAT Study Guide

Number Properties · Combinatorics · AWA Essay Template · GMAT Idioms

MBA Admissions

Average Scores & GPAs · Rankings · School Profiles

About Us

Platinum GMAT Prep provides the best GMAT preparation materials available anywhere, enabling individuals to master the GMAT and gain admission to any MBA program. We also provide hundreds of pages of free GMAT prep content, including practice questions, study guides, and test overviews.

rss GMAT Practice Question (One of Hundreds)
A test maker is to design a probability test from a list of 21 questions. The 21 questions are classified into three categories: hard, intermediate and easy. If there are 7 questions in each category and the test maker is to select two questions from each category, how many different combinations of questions can the test maker put on the test?
Correct Answer: A
The order of questions is not important and this is a combinations problem.
  1. In this problem order is not important. For example, the selection of question 1, 8 and 21 is the same as the selection of question 21, 8 and 1. Since order is unimportant, the combination formula applies.
  2. The formula for a combination is:
    nCr= n!/((n-r)!r!)
    where n is the total number of selections available and r is the number of items to be selected.
  3. Since the test maker must select a total of six questions and two questions from each category, the combination formula is used. Since there are 3 categories and two questions will be selected for each of the 3 categories, total number of combinations is:
    =7C2*7C2*7C2
  4. There are a total of (7C2)3 combinations.