Find the sum of all even numbers between 20 and 200.
200 - 20=180 all numbers
180/2 +1=91 terms
(F+(F+(N-1) X D)) X 1/2 X N=
(20+(20+(91-1) X 2)) X 1/2 X 91=10,010
+129847 Note that the number of even terms between 20 and 30 =
[30 - 20] / 2 - 1 =
10/2 - 1 =
5 - 1 =
4 ......so....
The number of even terms between 20 and 200 =
[200 - 20]/2 - 1 =
180/2 - 1 =
90 - 1 =
89
And.....we can arrange the numbers in such a way such that the sum of each pair = 198 + 22 =
220 .....and we will have 44 pairs of these plus [200 + 20] / 2 = 220/2 = 110 .......so.......
220*44 + 110 =
9790
