Explanation:
in 4 straight games ?
game 1 has a probability of 0.9 (= 90%).
for 2 games we have the probability of the first game, and now based on this we have to apply the probability of the second game.
in other words, the desired event has to happen in the first game AND then also in the second game.
since both probabilities are smaller than 1 (0.9), the total probability for 2 games must be less than the probability for 1 isolated game.
to combine such probabilities as "and" events, we have to multiply these probabilities.
so, the probability for 2 games is
0.9 × 0.9 = 0.9² = 0.81
and in the same way we get the probability to score the first goal in 4 games in a row :
0.9⁴ = 0.6561