Heat and Mass Transfer

At $25^\circ\text{C}$, the partial vapor pressure of water in equilibrium with a dehydrated food product is $2.25\text{ kPa}$. Pure water has a saturation vapor pressure of $3.17\text{ kPa}$ at the same temperature. The water activity ($a_w$) of the food is ________ (round off to 2 decimal places).