Explanation:
1)40, 120, 360, 1080, 32400
(it goes like add 80 then add 80*3 then 80*3*3 and then 80*3*3*3)
2)2, 8, 32, 128, 512
(it goes like 2, 2^3, 2^5, 2^7 and then 2^9)
3)1000, 500, 250, 125, 62.5
(keep dividing the sequence by 2)
4)256, 192, 144, 108, 81
(it goes like subtract (16*4) then (16*3) then (16*2) and then (16*1))
