I personally use RapidTables. Try it. It's quite simple.
Answer:
The value for 20th term is 10.
Step-by-step explanation:
First, you have to find the formula for the sequence.





Given that the formula of this sequence is an = -10n + 210. Next, you have to find 20th term :




(Correct me if I am wrong)
That expression can be written as
1 + 1·x