Look first at the range of the series: in first one is 26-23=3, in second one is 5. That is the first sign that S.D. of the second series is bigger. Look second at the distance of every number of the series from their mean. Mean is 25 and 27.5 respectively. When subtracting every number from the associated mean we get 2, 1, 0, 1, 1, 1 for first series and 2.5, 1.5, 0.5, 1.5, 2.5 for the second series. That is the second sign why SD of the second series is high likely greater.