Avideo game designer is evaluating a new release and issues a pre-release version to a set of testers. the testers spend an average of 12 minutes to complete the first level, with a standard deviation of 3.5 minutes. assuming a normal distribution for the data, 84% of players should complete the first level in less than how many minutes?

We call the minutes when most players complete the first level as X, as shown in the graph below

We are going to use the formula  to work out the value of X

We first need the value of Z. The probability given is 84% = 0.84
Reading on the z-table, the value of Z when probability 0.84 is 1

Then substituting into the formula of Z

1×3.5 = X - 12
X = 15.5

Answer is 15.5 minutes