Find the average of the first fifteen multiples of 11.

55 35.5 88 77

88

Sum of AP = \(\frac{n}{2}\) (2a + (n-1)d) Sum of 1st fifteen multiples of 11 = \(\frac{d15}{2}\) (2 x 11 + 14 x 11)                                                 = 1320 Average of 1st fifteen multiples of 11 = \(\frac{1320}{15}\)                                                       = 88