Answer:
Number of seats in theater=765
Step-by-step explanation:
A theater has 30 seats in the first row
33 seats in the second row
36 seats in the third row
and so on
the pattern of seats will be
30 33 36 39 42 45 48 51 54 57 60 63 66 69 72
The upper pattern is in arithmetic progression having n=15 terms
sum of arithmetic progression is
n(first term+last term)/2
hence, number of seats in theater= 15(30+72)/2
= 765
