As heat is transferred from the oven to the tray, imagine 90% of the heat is transferred. Now when the heat is transferred from the tray to the cake a smaller percentage is left out an maybe only 80% of the 90% is transferred to the cake. Note that when heat is transferred some of it is lost. So even though we take out the cake and tray from the oven which is set at a certain temperature, the temperature of the tray and the cake differs.
