Question

Please help!! Find the nth partial sum of the arithmetic sequence:
1.50, 1.45, 1.40, 1.35 . . . n=20

Answer 1

I think it is 0.55, is that correct?

Answer 2

not sure what you mean by nth partial sum

Answer 3

It just means add up the first n terms. In this case, n = 20, so add up the first 20 terms.

Answer 4

ok Is 0.55 correct, can you just tell me?

Answer 5

no, you have 20 terms which most are over 0.55, so it's definitely not possible to add positive numbers over 0.55 to get 0.55

Answer 6

sum of 20 terms = 10(2*1.5 + (20-1)*-0.5)

Answer 7

can you show me what to do? and how to get the answer?

Answer 8

* 10(2*1.5 + 19*-0.05) difference -0.05 not -0.5

Answer 9

Sum of first n terms = (number of terms)*(first term+nth term)/2

Answer 10

So

S = (n*(a1 + an))/2

Answer 11

r=1.45-1.50=-0.05
\[u _{1}=1.50\rightarrow u _{n}=1.55-n0.05\]\[\sum_{n=1}^{20}u _{n}=20\times1.55-0.05\times20\times21\div2=20.5\]Or your question is\[u _{20}=20\times(-0.05)+1.55=1.55-1=0.55\]

Answer 12

formula for sum n terms
= (n/2)(2a + (n-1)d)

Answer 13

So my answer, 0.55, is right then syderitic?

Answer 14

@cwrw238 is that right?

Answer 15

no, the answer isn't 0.55

Answer 16

then idk what is?

Answer 17

look, if you want the sum of the first 20 terms, then the answer is 20.5
if you want the 20th term of that sequence then the answer is 0.55

Answer 18

Plug n = 20, a1 = 1.5 and an = 0.55 into

S = (n*(a1 + an))/2

to find the sum

Answer 19

it says Find the nth partial sum @Syderitic

Answer 20

So @jim_thompson5910 I got 20.5. are u sure that is it?

Answer 21

English is not my primary language... sry

Answer 22

i would go for the 0.55 since you want the partial sum, so i'm guessing that's a term.

Answer 23

you got the right answer, I'm getting 20.5 as well

Answer 24

Ok ughhh idk if i should put .55 or 20.5

Answer 25

because they want the nth PARTIAL sum

Answer 26

0.55 is the 20th term, there's no way it's the 20th partial sum

Answer 27

i make it 20.5

Answer 28

are u guys positive?

Answer 29

it's 20.5

Answer 30

yes

Answer 31

the only thing i'm not positive of is the question itself...

Answer 32

i am putting 20.5

Answer 33

partial sum is confusing

Answer 34

If you really really want, you can add up the terms

1.5+1.45+1.4+1.35+1.3+1.25+1.2+1.15+1.1+1.05+1+0.95+0.9+0.85+0.8+0.75+0.7+0.65+0.6+0.55


These are the first 20 terms


And you'll get 20.5


So this confirms the answer.

Answer 35

thx