Answer:
0.54 or 54%
Explanation:
P( 1st but not second) = P(1st) - P(1st and Second) = 0.4 - 0.28 = 0.12 = 12%
P( 2nd but not first) = P(2nd) - P(1st and Second) = 0.7 - 0.28 = 0.42 = 42%
Probability of 1 of them (exactly one) = P( 1st but not second) + P( 2nd but not first) = 0.12 (12%) + 0.42 (42%) = 0.54 or also 54%.
Hope this helps!