The number of multiples of 19 < 775 = 775 / 19 = 40
And their sum = 19 (40)(41)/2 = 15580
The number of multiples of 5 < 775 = 770 / 5 = 154
And their sum = 5 (154)(155) / 2 = 59675
However....we must subtract out the sum of all numbers divisible by both 5 and 19.......this will equal all the multiples of 19 * 5 = 95.......so 775/95 = 8
So...the sum of these = 95 (8) (9)/2 = 3420
So...the total sum of all multiples of 5 or 16 less than 775 = [ 15580 + 59675 - 3420 ] = 71835
