This question doesn't come from GMAT text book. It just popped up in my mind during my study.
Given a set of letters (A,B,C), how many combinations of 4 letters are there, using both A and C at least once? You don't have to use all of them. Besides, (AACC), (CCAA),(ACAC),(CACA),(CAAC) and (ACCA) are all considered same.
I am kind of comfused during the caliculation. pLease help me.
Let me put it this way if I got it right:
We have 3 letters A,B and C. We want to form 4 letter combination from this letters, with condition that:
1. Order doesn't matter.
2. We should use at least once A and C, but not necessarily B.
How many such combinations are possible?
If it's so then, let's fix TWO letters AC, as they always should present.
We can easily right down all the possibilities.
Fixed AC as we must use them and any 3 left letter from the set:
New to the Math Forum?
Please read this: All You Need for Quant | PLEASE READ AND FOLLOW: 12 Rules for Posting!!!
GMAT Math Book | Triangles | Polygons | Coordinate Geometry | Factorials | Circles | Number Theory | Remainders; 8. Overlapping Sets | PDF of Math Book; 10. Remainders | GMAT Prep Software Analysis | SEVEN SAMURAI OF 2012 (BEST DISCUSSIONS) | Tricky questions from previous years.
Collection of Questions:
PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. ,11 Mixed Questions, 12 Fresh Meat
DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS; 9 Devil's Dozen!!!; 10 Number Properties set., 11 New DS set.
What are GMAT Club Tests?
Extra-hard Quant Tests with Brilliant Analytics