Question

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

Answer 1

Answer:

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

Step-by-step explanation:

tell me if this isn't 20 terms

Answer 2

Answer:

$S_{20}$ = 124

Step-by-step explanation:

The sum to n terms of an arithmetic series is

$S_{n}$ = $\frac{n}{2}$ [ 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

$S_{20}$ = $\frac{20}{2}$ [ (2 × 0.5) + (19 × 0.6) ]

     = 10 (1 + 11.4 )

     = 10 × 12.4

     = 124