Question 854209
Let the first term be a and the C.D be d.
The series is a,a+d,a+2d,a+3d

Accordingly, 
            a + a + 3d = 8 ......................................... (1)
            (a+d)(a+2d)= 15......................................... (2)
from (1),
          a= 8-3d/2
Now in (2),
           (8-3d/2 + d)(8-3d/2 + 2d) = 15
        => (8-3d+2d)/2*(8-3d+4d)/2 = 15
        => (8-d)(8+d) = 15*4
        => 64-d^2=60
        => d^2 = 64-60 =4
        => d = +2 or -2
a = 8-3.2/2
  = 8-6/2 
  =1
a = 8-3.(-2)/2
  = 8+6/2
  =14/2=7
The series is : (1,3,5,7) / (7,5,3,1)
Both are same. (ANS.)