Question 1124731
<br>
The sum of an arithmetic progression is the number of terms, multiplied by the average of the first and last terms:<br>
{{{S = n((a(1)+a(n))/2)}}}<br>
Plug in the given information:<br>
{{{385 = n((7+70)/2)}}}
{{{770 = 77n}}}
{{{n = 10}}}<br>
There are 10 terms in the A. P.