For which of the following sets of numbers do the mean, median and mode have the same value?

The mean of 12 observations is 75. If two observation are discarded, then the mean of the remaining observations is 65. What is the mean of the discarded observations?

If k is one of the roots of the equation x(x + 1) + 1 = 0, then what is its other root?

The geometric mean of a set of observations is computed as 10. The geometric mean obtained when each observations x_i is replaced by $\rm 3x_i^4$ is