Question 1166717: A theatre has 20 rows of chairs . The first row has 16 chairs , the second has 18, the third has 20 , and so on . In total , the theatre seats how many people?
Answer by dkppathak(439)   (Show Source):
You can put this solution on YOUR website! A theatre has 20 rows of chairs . The first row has 16 chairs , the second has 18, the third has 20 , and so on . In total , the theatre seats how many people?
solution
16,+18,+20.+...............+.20th
this is problem of sum of AP
a=16 d=2 n=20 we have to find s20=?
a20=a+19d
l (last term)=16+19x2
=16+38=54
sn=n(a+l)/2=20(16+54)/2
s20=20x70/2=700
total 700 seats
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