When working with a normal distribution, you can use the z-score to determine how many standard deviations away from the mean a certain data point is.
Given that the average price for houses in the area is $280,000 and the standard deviation is $12,000, we can use the z-score formula to find the price of a house whose z-score is 2.5:
z = (x - mu) / sigma
where x is the price of the house, mu is the mean price of houses in the area, and sigma is the standard deviation of the price of houses in the area.
In this case, we are looking for the value of x, which is the price of a house whose z-score is 2.5, so we can rearrange the formula to solve for x:
x = (z * sigma) + mu
x = (2.5 * $12,000) + $280,000
x = $350,000
So the price of a house whose z-score is 2.5 is $350,000
It's worth noting that the value of Z-Score 2.5 is considered an outlier, it is usually very rare to find houses that far from the average and standard deviation.