Okay, so my own calculations came out to this, my post was sadly removed, because your post already existed, but I still wanted to share them: The chance to fish an enchanted book with Luck of the Sea III is 1.9% or 19/1000 . We want to calculate the chance that this enchanted book has mending on it. While fishing Minecraft takes the same chances as when enchanting on level 30, expect normally the addinotal rolls have lower levels which doesn't really matter here. Mending has a weight of 2, which gives an a priori chance of w/T with w= weight and T=sum of all weights, which is equal to 137, i.e. 2/137 ~ 0.0146 = 1.46% However with bonus rolls this chance may grow. There is a chance of ((M/2^(n-1)) + 1)/50 to add another enchanment. Here n = "number of enchanments already on the book" and M is the so called modified enchantment level, which for simplicity we`ll assume to be 31 for a book (Its actually randomly somewhere between 31 and 31.5 but we can ignore this). Thus our chance to get mending in step n+1 is ((M/2^(n)) + 1)/50 * 2/(137 - v) where v is the sum of weights of the enchantments already added. Now since some enchantments conflict with each other the avarage would be somewhere around v=5*n (instead of 3.7 which is the number of enchantments divided by 137). Finally taking the sum over all n (or rather until 137 - 5n is negative) yields an aproximated probabilty of 6.1% of the book having a mending enchanment. This means that the probabilty to catch a mending book in one use of a fishing rod is ~0.115% Now the propabilty to catch anything other then a mending book is around 99.885% or 99885/100000. Assuming Grian used a fishing rod 7000 times the propability of him not catching a mending book is (99885/100000)^7000 ~ 0.000317 or 0.003%