Question

Determine the number of ways that two letters can be selected from {A, B, C, D} if the order in the sample is not to be considered.

List the possible samples.

Answer 1

N = 4C2

N = 6 ways

List of samples;

1. A,B

2. A,C

3. A,D

4. B,C

5. B,D

6. C,D

Explanation:

Since the order is not relevant, this is a combination case.

nCr = n!/r!(n-r)!

We are to select two letters from A,B,C,D (2 from 4)

The number of possible selections N can be given as:

N = 4C2 = 4!/2!(4-2)! = 4!/2!2! = 6

N = 6 ways

List of samples;

1. A,B

2. A,C

3. A,D

4. B,C

5. B,D

6. C,D