I am working on FRA. I looked into 20(b) figure 7 in schweser book. I tried to calculate defensive interval ratio, days sale outstanding and days inventory on hand. My calculation returns  52 days DSO, 75 days DHO and i am not sure how defensive  interval ratio calculated. However shwaser example return totally different number for 2016 year. Please let me know if you have explanations/ formula of calc.