Starting off we just need to divide the numbers by each other to see how they are increasing.
20÷8 = 2.5
50÷20 = 2.5
Seeing that our answer is 2.5 we need to multiply several times to reach our 10th term.
8, 20, 50, 125, 312.5, 781.25, 1953.125, 4882.8125, 12207.03125, 30517.578125
Meaning the 10th term is 30517.578125 or when rounded to a whole number 30,518
Checking
To check if the term is right you just need to keep dividing the numbers until your back at the starting number.
ex.
30517.578125 ÷ 2.5 = 12207.03125 (Which is the 9th term)