Simple

• Start with simple problems involving one- or two-digit numbers. For example, subtract five from seven to get two. Now, subtract five from 27. Write the two numbers on a piece of paper, with five on the bottom aligned with the ones digit, seven, for 27, on top. First, subtract five from seven to get two. There is nothing below the two in 27, so the result is two. Therefore, 27 minus five is 22. Now, subtract seven from 24. When you align the numbers, the ones digit for the number on the bottom, seven, is more than the ones on the top, four. This is where regrouping comes in: Borrow one from the tens digit and then do the subtraction. So 14 minus seven results in seven, which is the ones digit in the result. The two in the tens digit becomes one after the regrouping, and there is nothing underneath that digit, which means the tens digit of the result is one. Therefore, 24 minus seven is 17.
  
  

Intermediate

• Consider math problems involving two- or three-digit numbers. For example, subtract 45 from 72. This also involves regrouping: Borrow one from seven, then subtract five from 12 to get seven, which is the ones digit in the result. The remaining subtraction is six minus four, which is two. Therefore, 72 minus 45 is 27. Now, subtract 24 from 221. Regrouping is required: Subtract four from 11 to get seven; so the remaining subtraction is 21 minus two, which is 19. Therefore, 221 minus 24 is 197.
  
  

Advanced

• Advanced subtractions involve numbers with three or more digits. Most people use calculators to solve these problems, but they can also be done on paper. For example, subtract 125 from 394. First, use regrouping to subtract five from four to get nine, which is the ones digit in the result. So the remaining subtraction is 12 from 38. Subtract two from eight to get six, which is the tens digit in the result, and one from three to get two, which is the hundreds digit. Therefore, 394 minus 125 is 269.
  
  

Difficult

• Difficult subtraction problems involve multiple digits. However, you can still use the basic rules of regrouping. For example, subtract 1,245 from 2,733. Line them up by digits on a sheet of paper with 2,733 on top and 1,245 on bottom. First, use regrouping to subtract five from three to get eight, which is the ones digit in the result. The remaining subtraction is then 272 minus 124. Again, use regrouping to subtract four from two to get eight, which is the tens digit in the result. The remaining subtraction is 26 minus 12, which is 14. Therefore, 2,733 minus 1,245 is 1,488.