For every positive integer n, the nth term of sequence is given by an= 1/n - 1/(n+1). What is the sum of the first 80 terms?
Choices.
A) 1	B) 21	C) 40/41	D) 80/81	E) 160/161
a1 = 1 - 1/2   a2 = 1/2 - 1/3   a3 = 1/3 - 1/4   etc...   a80 = 1/80 - 1/81   The sum of these terms is 1-1/81 = 80/81   The answer is 80/81.
<result>D</result>
For every positive integer n, the nth term of sequence is given by an= 1/n - 1/(n+1). What is the sum of the first 80 terms?