Question 391680
The mean of 19 numbers is 1600, so


{{{(sum(a[i], i = 1, 19))/19 = 1600}}}


{{{sum(a[i], i = 1, 19) = 1600*19 = 30400}}}


If we let {{{a[20] = 2000}}}, then


{{{sum(a[i], i=1, 20) = sum(a[i], i=1, 19) + 2000 = 30400 + 2000 = 32400}}}


The mean of these twenty numbers is just 32400 divided by 20, or 1620.