Question

To begin the half-time performance, a high
school band marches onto the football field in
a pyramid formation. The drum major leads
the band alone in the first row. There are two
band members in the second row, three in the
third row, four in the fourth row, and so on.
The pyramid formation has 25 rows.
How many members does the band have?

Answer 1

Sum of triangular numbers

Answer 2

Well u can think of it as an arithmetic sequence

1,2,3,4,5,...,25

Answer 3

Then u can find the sum of this arithmetic sequence

http://www.purplemath.com/modules/series4.htm

Answer 4

Do u know what n, an and a1 are?

Answer 5

is n 25?

Answer 6

Yes

Answer 7

an would be 25?

Answer 8

Yes

Answer 9

a1 would be 1?

Answer 10

Yes. Now plug it into that formula

Answer 11

325

Answer 12

Correct