I have a the below chart that compares the successes and rejections when someone arrives. I want to add an expression that gives me the % rejection of the cumulative values. For example, if I am looking at the week of October 12th I want it to divide 498/(498+3942)= 11.2%, then if I look at the week of October 19th it divides the cummulatives 526/(526+4014)=11.59%. I know it has to deal with a rangesum, but I cant come up with the correct formula. Any help would be much appreciated!