Question

In an arithmetic sequence, the 7th term is 30, and the 11th term is 60. What is the 21st term of this sequence?

Answer 1

135

Explanation:

7th term ;a + 6d = 30

11th term; a + 10d = 60

solving simultaneously,a= -15 ,d= 7.5

21st term = a + 20d= 135