find sn for the arithmetic sequence a1=29, n=80 and an=201?

Question

answers:
18,400
9,200
310
230

Answer 1

We know that the sum is

n * (a1 + an) /2 = 80*230/2 = 9200

Answer 9200

Answer 2

I am assuming here that the an you gave is actually the last term in the sequence.

The equations for calculating Sn are:
1) Sn = n/2 [2a + (n-1) d]

2) Sn = n/2 [ a + l ]

where: n is the number of terms
a is the first term of the sequence
d is the common difference
l is te last term is the sequence

for this problem, it's easier to use the 2nd equation as you already have the first and last term.

Replacing in the equation, you will get the following:

Sn = n/2 [ a + l ]
= 80/2 [ 29 + 201 ]
= 40 [ 230 ]
= 9200

Hope this helps.

Answer 3

Sn = n(a1 + an)/2
Sn = (80)(29 + 201)/2
Sn = (80)(230)/2
Sn = (80)(115)
Sn = 9200

Answer 4

310