math
posted by Rusty .
On the 1st day the movie opened 35 people saw it. On the 2nd day 16 more people came than on the 1st day so that 86 people had seen the movie after the second day. On the 3rd day 67 people came, 16 more than on the 2nd day, If each day 16 more people saw the movie than the day before, on what day would 700 people have seen the movie?

Isn't this an arithemetic sequence?
distance=16, first term 35
Don't you have a formula for the sum of n terms? Use that, find n. 
You are dealing with an arithmetic series.
a = 35, d=16
Sum(n) = (n/2)(2a + (n1)d)
700 = (n/2)(70 + 16(n1))
1400 = n(70 + 16n  16)
1400 = 54n + 16n^2
16n^2 + 54n  1400 =0
solve the quadratic.
But remember that n must be a positive whole number.
Also check my arithmetic, I have no pencil, paper or calculator with me at the moment.