1/16 + 1/8 + 1/4 +...=x. Nilai x adalah...

1/16 + 1/8 + 1/4 = x    
x = 1/16 + 1/8 + 1/4              (samakan penyebut jadi 16)
x = 1/16 + 2/16 + 4/16
x = 7/16

a = 1/16
r = 2

S4 = a . (r⁴-1)/(r-1)
S4 = 1/16 . (16-1)/(2-1)
S4 = 15/16