What is the probability of getting 3 heads in a row on a trick coin where heads comes up twice as often as tails?

In how many throws? Just 3? Then it's 2/3^3

Multiply the individual probabilities: P(1st. Head)*P(2nd head)*P(3rd head). SInce the coin is a trick coin, the P(Head) for any one toss will not be its usual value of 1/2.