Question 1204442
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n = number of terms


Sn = sum of first n terms of arithmetic progression (AP)
Sn = (n/2)*(first term + nth term)
507 = (n/2)*(1 + 77)
507*2 = 78n
1014 = 78n
n = 1014/78
n = 13


Answer: <font color=red>13 terms</font>
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