This is how it's taught at my local school, but it's a bit hidden, because the the 7 is "broken apart", not "subtracted": 61 - 17 = 60 + 1 - (10 + 1 + 6) = (60

This is how it's taught at my local school, but it's a bit hidden, because the the 7 is "broken apart", not "subtracted": 61 - 17 = 60 + 1 - (10 + 1 + 6) = (60 - 10) + (-6) "Breaking apart" is equivalent to subtraction, but feels different when doing mental calculation.