<PRE><B>Question 880057</B>


S = ½(2a + (n-1)d)n
S = ½(40 + 4*17)18
S = 9(40 + 68)

s=9*108=972 seats in 18 rows 
row seats total
1   20    20
2   24    44
3   28    72
4   32    104
5   36    140
6   40    180
7   44    224
8   48    272
9   52    324
10  56    380
11  60    440
12  64    504
13  68    572
14  72    644
15  76    720
16  80    800
17  84    884
18  88    972
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