An infinite geometric series has a common ratio $-1/5$ and sum $16.$ What is the first term of the series?
From the forumla for an infinite geometric series, the first term is 28/5.
Sum = F / [1 - ( - 1/5)]
16 = F / (6/5)
16 = F x (5/6)
16 = 5F / 6 Cross multiply
5F = 16 * 6 = 96
F = 96 / 5 - which is the first term
+109 
