From 7 positive numbers and 7 negative numbers, how many groups of 4 numbers, yielding a positive product, can be formed? Answers: A) 720 B) 625 C) 327 D) 960 E) 511
The number of ways to choose 4 positive numbers is 7C4 = 35.   The number of ways to choose 4 negative numbers is 7C4 = 35.   The number of ways to choose 2 positive and 2 negative is 7C2*7C2 = 21*21= 
<gadget id="calculator">21*21</gadget>
<output>441</output>
441.   The total number of groups is 35+35+441= 
<gadget id="calculator">35+35+441</gadget>
<output>511</output>
511.   The answer is 511.
<result>E</result>
From 7 positive numbers and 7 negative numbers, how many groups of 4 numbers, yielding a positive product, can be formed?