in a 20-row theater,the number of seats in a row increases by three with each successive row.the first row has 18 seats. a:write an arithmetic series to represent the number of seats in the theater. please help im stuck!

Question

in a 20-row theater,the number of seats in a row increases by three with each successive row.the first row has 18 seats.         a:write an arithmetic series to represent the number of seats in the theater.           please help im stuck!

anonymous · Answer

This is easy. Make a chart, it should be very clear to you after you see a chart of what you are trying to look at.

anonymous · Answer

would i not need a formula?

anonymous · Answer

There is a way, but I find it more clear to see by using a chart.

anonymous · Answer

i dont know how to even set up the equation

anonymous · Answer

Make a chart, it will help you much more.

jdoe0001 · Answer

@catrina so, I assume you've covered arithmetic sequences?

anonymous · Answer

how do i set the chart up?as :
1st row-18 (+3)
2nd-21(+3)   
...
20th row-75

anonymous · Answer

Yes, that is correct.

anonymous · Answer

im helping my boyfriend i have already done this but it was 2 years ago and i cant remember a thing

jdoe0001 · Answer

hehe

anonymous · Answer

ok now how do i set up the equation to show the number of seats?

jdoe0001 · Answer

well, the sum of a partial sequence is $\bf \Large s_n = \cfrac{n}{2}(a_1+a_n)$

anonymous · Answer

so thts the formula?

jdoe0001 · Answer

for the sum from the 1st term up to the Nth term, yes

jdoe0001 · Answer

hmm, but you're not being asked on the equation itself, so much as to write the sequence itself, I think

anonymous · Answer

ok so basicly i wud set it up as 
 S20=20/2(18+20)?

jdoe0001 · Answer

well, the 1st term is 18, the 20th term is not 20 though
but I gather is not what's being asked
what's being asked is, to "write an arithmetic serie"
not to give the total amount of seats in the theater

anonymous · Answer

yea but it says write one to represent the total amount

jdoe0001 · Answer

well, well
what's the common ratio in the sequence  you think?

anonymous · Answer

it says 3

jdoe0001 · Answer

so to find the 20th term, the Nth term, n = 20,  $\bf \Large a_n = a_1+(n-1)d$
n = the nth term
d = common ratio

anonymous · Answer

ok,so
a20=18+(20-1)3   ?

jdoe0001 · Answer

hmm, i notice up above you already had it as 75, so , just use the Sum equation then :)

jdoe0001 · Answer

"catrina 
ok so basicly i wud set it up as 
 S20=20/2(18+20)?"

yes

anonymous · Answer

ok thnx