9. round 12.079 to two decimal places,

(a)11

(b)12

Step-by-step explanation:

The first term, a = 1

The last term, l=121

Sum of the series,

Given an arithmetic series where the first and last term is known, its sum is calculated using the formula:

Substituting the given values, we have:

(a)There are 11 terms in the arithmetic progression.

(b)We know that the 11th term is 121

The nth term of an arithmetic progression is derived using the formula:

Therefore:

121=1+(11-1)d

121-1=10d

120=10d

d=12

The common  difference between them is 12.