There's a nice rule that says, "In a set where the numbers are equally spaced, the mean will equal the median."
For example, in each of the following sets, the mean and median are equal:
{7, 9, 11, 13, 15}
{-1, 4, 9, 14}
{3, 4, 5, 6}

There's another nice rule that says, In a set where the numbers are equally spaced, the mean = (largest value + smallest value)/2

The multiples of ten from 10 to 190 inclusive are equally spaced, so the median = the mean

So, the mean = median = (10 + 190)/2 = 100

Answer: C

Cheers,
Brent