the formula for p(a or b) is:

p(a or b) = p(a) + p(b) - p(ab)

p(a) = the probability of rolling three of a kind:

P(a) = 6/(6^3) = 1/6^2

p(b) = the probability of rolling a sum that is an odd number:

p(b) = 1/2

p(ab) is the probability of both occurring at the same time, rolling 3 of a kind whose sum is an odd number:

p(ab) = 3/6^3

p(ab) = 1/(2*(6^2))

lets plug the values into

p(a or b) = p(a) + p(b) - p(ab)

p(a or b) = 1/6^2 + 1/2 - 1/(2*(6^2))

by calculating we find:

p(a or b) = 0.5139

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the probability of Derek rolling three of a kind or a sum that is an odd number is 0.5139.