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In a certain theater, the first row has 16 seats and the nex

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In a certain theater, the first row has 16 seats and the nex

by Max@Math Revolution » Tue Mar 15, 2016 5:50 pm
In a certain theater, the first row has 16 seats and the next row has 2 more seats than previous row. If the last row has 64 seats, what is the total number of seats?

A. 640
B. 720
C. 1,000
D. 1,200
E. 1,240


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by sandipgumtya » Thu Mar 17, 2016 9:02 am
We can apply AP series formula here.First term as 16 and last term 64.We get the no of terms as 25.Now the sum formula.
Sum=(25/2)*(2*16+24*2)=1000.Ans-C

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by Max@Math Revolution » Sat Mar 19, 2016 9:58 pm
In a certain theater, the first row has 16 seats and the next row has 2 more seats than previous row. If the last row has 64 seats, what is the total number of seats?

A. 640
B. 720
C. 1,000
D. 1,200
E. 1,240


A1=16, A2=16+2, A3=16+2*2,.....,An=16+(n-1)2=2n+14. In order make 2n+14=64, n should be 25. That is, there are 25 rows. Thus, in total, 25(16+64)/2=1,000 is derived. The answer is C.
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