The first term of an infinite geometric series is 21 . The second term and the sum of the series are both positive integers. The possible value(s) of the second term can be

Step-by-step solution

Let the series be 21,21 r , 21 r ^2, . Sum = 21 1-r is a positive integer also 21 r is a positive integer S = (21)(21) 21-21 r as 21 r N hence 21-21 r must be an integer also 21 r 21 Hence 21 - 21r may be equal to 1, 3, 7 or 9 (think!) i.e. must be a divisor of (21)(21) Hence, 21-21 r =1 or 3 or 7 or 9 21 r=20,18,14 or 12