650-583 can be worked out in different ways.
583 is 17 short of 600 and 650-600=50. But we’re not taking away as much as 600, so we add 50 to 17=67. Therefore 650-583=67.
Here’s another way:
650=600+50 and 583=500+80+3.
To do the subtraction we have to work out:
600+50-500-80-3.
Work out 600-500 first: 100.
So now we have:
100+50-80-3,
100-80=20, leaving us with:
20+50-3,
20-3=17 leaving us with:
50+17=67, the answer.