Quantitative Aptitude

Arithmetico-geometric series: $S = \frac{a}{1-r} + \frac{dr}{(1-r)^2} = \frac{1}{1 - 1/3} + \frac{1 \times (1/3)}{(1 - 1/3)^2} = \frac{1}{2/3} + \frac{1/3}{4/9} = \frac{3}{2} + \frac{3}{4} = \frac{9}{4} = 2.25$.