## BrittanyFrench 2 years ago Can some explain to be on what to do with a question like this: Suppose a movie theater has 42 rows of seats and there are 29 seats in the first row. Each row after the first has 2 more seats than the row before it. How many seats are in the theater?

1. BrittanyFrench

I know it's using gemoetric or arithmetic stuff

2. Saikam

ok. so can u tell me how many seats in the second row?

3. BrittanyFrench

31 right?

4. itsmylife

first row has 29 common difference is d=2, your a=29 , d=2 therefore in 42 rows there are total of $Sn=\frac{ n }{ 2 }(2a+(n-1)d)=\frac{ 42 }{ 2 }(2*29+(42-1)2)$ you can calculate now

5. itsmylife

it should be 2940 seats

6. Saikam

yea. 29 + 2 and in the third its 29 + 2 + 2 = 29+4 in the fourth, it is 29 + 6 and so on... so the nth row would contain 29 + (n-1)*2 This is the general term of an A.P. and you are asked to find the sum of the first 42 terms.

7. BrittanyFrench

Dang that's alot of seats,and yeah I calculated that! Thank you..