will medal. A field house a section where the seating can be arranged so the first row has 9 seats, the second row has 11 seats, the third row has 13 seats and so on.. if there is sufficient space for 26 rows in the section, how many seats are there in that entire section?

Question

anonymous · Answer

a collection of marbles is set up into 5 rows. the first row has 125 marbles, and each row after that one has 4 less marbles than the preceding row. how many total marbles are there in the 3rd row

danjs · Answer

each row increases # of seats by 2 chairs, one on each end, forming a triangle

danjs · Answer

for example first 3 rows

9 + 11+13+15+17 .....(26 numbers to add up)

danjs · Answer

sum of the ODD numbers starting at 9, (26 numbers)

danjs · Answer

Odd number for row n,  

a(n) =  2*(n+3)+1 

For n is the row number starting at n = 1, to n=26, need to sum them all

danjs · Answer

a(1) = 2*(4) + 1 = 9
a(2) = 2*(5) + 1 = 11
a(3) = 2*(6) + 1 = 13
...
...
...
a(26) = 2*(29) + 1 = 59

danjs · Answer

are you doing series in class?

anonymous · Answer

no, this a review from way back and i totally forget

danjs · Answer

use 

$\large\color{blue}{a(n) = 2*(n+3)+1  }$     

for n=1 up to n=26
and add all the numbers
It is just the sum of 26 odd numbers starting with 9

9+11+13+15+17+ .......59

anonymous · Answer

so the answer would be 59?

danjs · Answer

no, the 26th row has 59 chairs.

you have to add together 26 odd numbers, starting with 9 and up to 59

danjs · Answer

9 + 11 + 13 + 15 + 17 + 19 + 21 + 23 +...........up to + 59

anonymous · Answer

884

danjs · Answer

$$\sum_{n=1}^{26}[2*(n+3) + 1]$$ = 884

danjs · Answer

yep that is what i got

danjs · Answer

$$\large\color{blue}{\sum_{n=1}^{26}2*(n+3)+1 = 884 }$$

anonymous · Answer

a collection of marbles is set up into 5 rows. the first row has 125 marbles, and each row after that one has 4 less marbles than the preceding row. how many total marbles are there in the 3rd row
Help with this one?

danjs · Answer

First row 125
Second - 125 - 4 = 121
third - 121 - 4 = 117

danjs · Answer

125 - 4(n-1)

n = row number

danjs · Answer

n=1    125
n=2    121
n=3    117

anonymous · Answer

i got 113

danjs · Answer

first row has 125 , each row is 4 less than the previous, 

second row 125-4
third row 125-4-4

danjs · Answer

First row has 125
second row has 121
Third row has 117
Fourth Row has 113
Fifth Row has 109