varianza

clase	f	pm	Pmxf	x-media	(x-media) 2	(x-media)2 xf
0-1	36	0.5	18	-2.4	5.76	207.36
2-3	48	2.5	120	-0.4	0.16	7.68
4-5	66	4.5	297	1.6	2.56	168.96
total	150		435			384

Media= 2.9

Varianza =384/150=2.56