1. Use this formula to obtain the number of integers:
(last - first) / increment + 1
(20- 2)/2 + 1 = 10 avg = (20 + 2) / 2 = 11 even integers
sum = 10* 11 = 110
same for odd
(19 - 1)/2 + 1 = 10 odd integers
(19 + 1)/2 = 10
10 *10 = 100
110 - 100 = 10
2. 1250:

4000
ratio: 6x::2x::1x
37500/1250 = 30
(6)*(5) = 30
so x is 5
since 4000 is the ratio of 1x, it is 1*5 = 5
3. 660 + 30(x) = 780 -10(x)
x = 3
so it is 1993