A patisserie wants to determine if baking a particular cake at a higher temperature for shorter will produce a lighter cake, as measured by the density of the cake. A trial was conducted, with twenty batters prepared the same way. Each batter ws divided into two equal parts, and one of these was baked at the higher temperature while the other was baked at the usual temperature. The cakes baked at the higher temperature were lighter by 20 on average, and the standard deviation of the differences in the density was 18. What is the p-value for a test of the appropriate hypotheses? Give your answer to 4 decimal places.