Question

And arithmetic sequence has a first term of 10 and the sixth term of 40. What is the 20th term of the sequuence?

Answer 1

The general form of the n-th term = a + (n-1)d

Here we are given the 1st term (a) = 10

6th term = 40

We need to find the 20th term.

Let's find the common difference.

6th term = 10 + (6 - 1) d

6th term is 40, so

40 = 10 + (6 -1)d

40 -10 = 5d

30 = 5d

d = 30/5

d = 6

The common difference is d = 6.

20th term = a + (n -1)d

= 10 + (20 -1)6

= 10 + 19*6

= 10 + 114

20th term = 124