A slab of dry wood of 4-in. thickness and sealed edges is exposed to air of 40% relative humidity. Assuming that the two unsealed faces of the wood immediately jump to an equilibrium moisture content of 10 lb H20 per 100 lb of dry wood, determine the time for the moisture to penetrate to the center of the slab (2 in. from either face). Assume a diffusivity of water in the wood as 8.3 x l0-6 cm2/s.