Answer:
21 different tests are required for every possible pairing of wires.
Explanation:
Number of colour-coded wires, i.e n = 7
Number of tested wires at a time, r = 5
By combination,
C(n, r) = n!/r! (n-r)!
n! = 7! = 7x6x5x4 3x2x1
C(7, 5) = 7!/5! (7 - 5)!
C(7, 5) = 7!/5! x 2!
C(7, 5) = 7 x 6 x 5!/5! x 2
C(7, 5) = 42/2
C(7, 5) = 21
∴ 21 different tests are required for every possible pairing of wires.
