A linear combination is a contrast if the sum of its coefficients is equal to zero. Let's check each linear combination:
(i) $\mu_{1}+3 \mu_{2}-4 \mu_{3}$: The coefficients are 1, 3, and -4. Their sum is 1 + 3 - 4 = 0, so this is a contrast.
(ii) $.3 \mu_{1}+.5
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