Question

Given {2.4, 3.9, 5.4, 6.9, 8.4, ...}

(a) Find the 111th term.

(b) Find the sum of the first 111 terms of the sequence.

Answer 1

$a=2.4$

$$d=3.9-2.4=5.4-3.9=6.9-5.4$$

$$=8.4-6.9=1.5$$

a)

$$a_{111}=a+110d=2.4+110(1.5)=167.4$$

b)

$$S_{111}=111\cdot\dfrac{a+a_{111}}{2}=111\cdot\dfrac{2.4+167.4}{2}$$

$$=9423.9$$