Answer: 1/12
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Work Shown:
A = probability of getting tails
A = 1/2
B = probability of rolling a "3" on a six-sided die
B = 1/6
C = probability events A and B happen together
C = A*B ... works since the events are independent
C = (1/2)*(1/6)
C = (1*1)/(2*6)
C = 1/12
As a decimal, this is approximately 1/12 = 0.0833 which converts to 8.33%; I would stick to the fraction format since it's the most exact.