Arithmetic Progression (AP) - In the question, it will entail no sequence numbers, it will be based on two terms. The 8th Term and the 16th Term

Question

If the 8th term of an AP is 36 and the 16th term is 68

Find: a) the first term. b) the common difference. c) The 20th term.

Answer 1

$$8^{th} term=a_1+7d=36\\16^{th} term=a_1+15d=68$$ It follows $$d=\frac{68-36}{8}=4$$ Hence $$a_1=36-7\cdot 4=8\\a_{20}=a_{16}+4\cdot4=68+16=84$$