21
40.
80
22
It is possible to find a quartic equation (power 4) so that any fifth number is the next in the sequence. The cubic that fits these is Un = (n3 + 17n + 30)/6 for n = 1, 2, 3, ... and therefore, the next term is 40.
Double it every time and so the next number will be 80
If you mean: 5 10 20 40 then it is 80
40 5 10 20 40 80 160.......double the number each time.
16
The pattern is to divide by 5, so the next number would be 40
If the last number is 1/3 (it should be), the next number is 5 and 1/3
The next number should be 80.
70