Let X be the random variable representing the change in the number of employees for the next year. We can find the expected value of X as:
E(X) = (probability of gain) * (gain) + (probability of loss) * (loss)
We know that the store will increase by 300 employees, and there is a 70% chance that the increase will be 400 employees. Therefore, the probability of gaining 400 employees is 0.7, and the gain is 400.
We also know that there is a 10% chance that the number of employees will decrease by 500. Therefore, the probability of losing 500 employees is 0.1, and the loss is -500.
Substituting these values into the formula for the expected value, we get:
E(X) = (0.7)(400) + (0.1)(-500)
E(X) = 280 - 50
E(X) = 230
Therefore, the expected gain or loss of employees for the next year is 230 employees. We expect the store to gain 230 employees on average.