2020 · Q14
The sum of all possible products taken two at a time out of the numbers ±1, ±2, ±3, ±4, ±5 is
Elementary MathematicsNumber System
- A0
- B−30
- C−55
- D55
Explanation
The ten numbers sum to 0. The sum of all pairwise products equals ((sum)^2 - sum of squares)/2 = (0-110)/2 = -55. Hence option (C).