Question

Find the sum of the first 20 terms of the arithmetic series 0.5 + 1.1

+ 1.7 + 2.3 + 2.9 + ..
Hint: Sn= n(9/4")

Answer 1

`S_(20)` = 124

Explanation:

The sum to n terms of an arithmetic series is

`S_(n)` =
`(n)/(2)` [ 2a₁ + (n - 1)d ]

where a₁ is the first term and d the common difference

Here a₁ = 0.5 and d = a₂ - a₁ = 1.1 - 0.5 = 0.6 , then

`S_(20)` =
`(20)/(2)` [ (2 × 0.5) + (19 × 0.6) ]

= 10 (1 + 11.4 )

= 10 × 12.4

= 124

Answer 2

0.5+1.1+1.7+2.3+2.9+3.5+4.1+4.7+5.3+5.9+6.5+7.1+7.7+8.3+8.9+9.5+10.1+10.7+11.3+11.9

Explanation:

tell me if this isn't 20 terms