Basic probability question?

Question

if i have a 10% chance of succeeding at a certain task and i perform that task 4 times, what is the chance that i have succeeded at the task at the end of the 4 tries?

(show your work! :))

Answer 1

You might succeed 0, 1, 2, 3, or 4 times.

Except for the 0 case, you have at least one success.

The chances of failing all 4 times are

.9 x .9 x .9 x .9 = .6561

The remaining chances are .3439

So you have a 34.39 percent chance of succeeding at least once.

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Answer 2

Assuming that you don't get better with practice, the chances are 40 percent.  In probability, for AND you multiply the fractions and for OR you add them.  This is an OR because you only need success in either attempt 1, 2, 3 or 4.  So you add 1/10 + 1/10 + 1/10 + 1/10 and you get 4/10 which is 40 percent.