High School

If the last term of an arithmetic progression (AP) with 30 terms is 119, and the 8th term from the end (towards the first term) is 91, find the common difference of the AP.

Hence, find the 20th term of the AP.

Answer :

Final answer:

The common difference of the arithmetic progression is 1. The 20th term of the AP is a + 19.

Explanation:

To find the common difference, we can use the formula for the nth term of an arithmetic progression:

a_n = a + (n-1)d

Where a_n is the nth term, a is the first term, n is the number of terms, and d is the common difference.

In this case, we are given that the last term is 119 and the 8th term from the end is 91. Using the formula, we can substitute these values in and solve for d:

119 = a + 29d

91 = a + 3d

By subtracting the second equation from the first, we get:

28 = 26d

d = 1

Therefore, the common difference is 1.

To find the 20th term of the AP, we can use the formula again:

a_20 = a + (20-1)d

Substituting in the values, we get:

a_20 = a + 19