If 400 workers in a plant are exposed to the following concentrations of ammonia for the given number of hours, cumulative, how many deaths will be expected? 500 ppm for 1 hr, then, 1000 ppm for 2 hr, then, 2000 ppm for 3 hr, then, 200 ppm for 2 hr Use Excel sheet to calculate probit, Y. Use Polymath to calculate P, using the equation: P= 50 [1+((Y-5)/|Y-5D) erf ((Y-5)//2)]