+128475 We have this arithmetic series
10 + 12 + 14 + ......+ ??? = 220
The sum of an arithmetic series is given by :
S = (n / 2) [ 2a + (n - 1) * d ]
Where a is the first term, n is the number of terms [ and the number of rows in this case ] and d is the difference between terms
So we have
(n / 2) [ 2(10) + ( n - 1) * 2 ] = 220 multiply both sides by 2
n [ 20 + 2n - 2 ] = 440
n [ 18 + 2n ] = 440
2n^2 + 18n - 440 = 0 divide through by 2
n^2 + 9n - 220 = 0 factor
(n + 20) ( n - 11) = 0
Set eacn factor to 0 and solve for n and we get that
n = -20 [ reject ] or
n = 11 [ accept ]
So....11 rows
