Subtracting 2 digits from 3 digits (renaming)
Hi there, I have a question about subtraction. I know it pretty well, but I'm having problems with certain questions. So take this question for example: 155 subtracted by 66. So, for that question I got the answer: 99. I know that when solving it, the 1 hundreds gets renamed to 0, the 5 tens becomes 15 and the one 5 becomes 15 as well. But when I checked my answer, I found out that's it's wrong because the correct answer is 89. I tried to solve it others ways but, no matter what I do, I keep getting 99. So what I don't understand is, why is it that when I subtract the 15 from 6 in the ones place it equals to 9 but, when I do it in the tens place, it's supposed to equal to 8? I also have this problem with this question: 191 subtracted by 72. I got: 118 but the correct answer is 119. I renamed 9 tens to 8, and 1 ones to 10, I know that 10 subtracted by 2 is 8, so I'm really confused to why the answer is 119. I've been trying to find others ways of getting the correct answer, but I still end up with 118. Can anyone please explain this to me? Thank you so much for your time.