Maths strategy

At school Mrs.R taught us 2 maths strategy's. One of them is rounding and adjusting the other is adding the parts.
How you do rounding and adjusting is say the sum is 56+79=?[witch is very hard shh] what you do is you would round up 79 or 56 I am going to round up 79 to 80, so then I add 56+80=136 but, then I have to take away 1 and it will equal to 135!
Adding the parts is when you add the parts to 56+79, so you would do this,
56
+ 79
= you add up 6 and 9 witch equals15 so you carry the one and put it above the 5 and then put the 5 at the bottom, then add 5,7 and 1 witch equals 13 so then you add 13 and 5 witch equals to 135!