In a study of reaction times to a specific stimulus, a psychologist recorded these data (in seconds).
Class limits Frequency
2.1–2.7 .......12
2.8–3.4 .......13
3.5–4.1 .........7
4.2–4.8 .........5
4.9–5.5 .........2
5.6–6.2 .........1
Find the variance and standard deviation.