Prime numbers are numbers that has only two factors (i.e 1 and itself). They are numbers that are only divisible by 1 and their selves. First four Prime numbers greater than 10 are 11, 13, 17 and 19

  Average = sum of numbers / number

  = \(frac{(11 + 13 + 17 + 19)}{4}\)

  = \(\frac{60}{4}\)

  = 15