Easy ways to calculate sums

Today I learnt that there are easy ways to calculate sums in your head.
One: Rainbow facts, you find sums that add up to 10, 100, 1000, 10000 and so on, like 1 & 9, 2 & 8, 3 & 7, 4 & 6 & 5 & 5.
Two: Rounding and Adjusting, you round the numbers into an easier sum, like 163+140 that is hard to work out so you can round it to 150+150, the other ones left out are added together so 163-150=13 and 140+10=150 so 150-140=10 so 13-10=3 so the answer is 203
Three: Adding the parts, for example 653=326, 600+300=900, 50+20=70, 6+3=9, so 900+70=9=979