A stratified soil deposit consists of three layers. The permeabilities of the layers are 8.5 x 10-4, 38 x 10-4 and 12 x 10-4 cm/sec; the thickness of the layers are 6.2 m , 3.5 m and 10 m respectively. Then the average permeability of the deposit perpendicular to plane is
1
1.19 x 10-3 cm/sec
2
2.178 x 10-4 cm/sec
3
1.80 x 10-2 cm/sec
4
3.17 x 10-5 cm/sec