In a store 6 different CDs are there. If John can buy 2 CDs, how many cases that he can buy are there?
Choose the correct answer
A) 12 B) 15 C) 18 D) 21 E) 24
Let CDs are A, 15, C, D, E, F   He may choose any pair as mentioned below   A15, AC, AD, AE, AF = 5 cases   15C, 15D, 15E, 15F = 4 cases   CD, CE, CF = 3 cases   DE, DF = 2 cases   EF = 1 case   Total cases = 5+4+3+2+1= 
<gadget id="calculator">5+4+3+2+1</gadget>
<output>15</output>
15   Answer: Option 15
<result>B</result>
In a store 6 different CDs are there. If John can buy 2 CDs, how many cases that he can buy are there?