1.6 Add and subtract large numbers
Addition
We add large numbers in the same way as we add smaller numbers:
Activity 6: Adding whole numbers
Complete the following tasks without using a calculator:
 8 936 + 453
 3 291 + 2 520
 35 + 214 + 9 963
 28 550 + 865
 243 552 + 64 771
 698 441 + 323 118
Remember you can check your calculations using the inverse method, which means using the opposite type of sum to check that your answer is correct. For example, you can use subtraction to check that an addition calculation is correct:
630 + 295 = 925 (addition)
925 – 295 = 630 (subtraction to check)
Answer
The answers are as follows:
 9 389
 5 811
 10 212
 29 415
 308 323
 1 021 559
Subtraction
There are different methods that can be used to subtract numbers. You need to find the method that works for you.
Decomposition method
For example:
843 – 266
Follow the following steps:

 a.Start with the units: subtract 6 from 3. (This can’t be done.)
 b.There are four tens in the tens column. One of these can be given to the units column.
 c.If 10 is added to the original 3 we now have 13 in the units column: 13 – 6 = 7.
 d.7 is placed on the answer line in the units column.

 a.Now move on to the tens column: subtract 6 from 3. There are only three tens left, because one 10 was added to the units column. (This can’t be done.)
 b.There are eight hundreds in the hundreds column. Taking one from the hundreds column and moving it to the tens column makes 13 in the tens column: 13 – 6 = 7.
 c.7 is placed on the answer line in the tens column.

 a.There is now a 7 in the hundreds column.
 b.Subtract 3 from 7: 7 – 2 = 5.
 c.This is placed on the answer line in the hundreds column.
The final answer is 577.
You need to be careful when trying to subtract with zeros; for example, 800 – 427. The following video shows the decomposition method in full, including dealing with zeros:
‘Borrow and pay back’ method
For example:
765 – 39
Follow the following steps:
 Start with the units. You cannot subtract 9 from 5.
 You borrow 10 to make it 15.
 Now you have borrowed, you must ‘pay back’ by adding 1 to the tens column of the number that you are subtracting. This increases both numbers by ten (5 + 10 = 15 and 39 + 10 = 49). The difference stays the same.
Activity 7: Subtracting whole numbers
Complete this activity using the subtraction method that you are most familiar with. Do not use a calculator.
 9 965 – 742
 8 163 – 7 481
 27 364 – 9 583
 600 987 – 4 500
 975 046 – 74 308
 587 342 – 369 453
Remember you can check your calculations using the inverse method, which means using subtraction to check that your answer to an addition calculation is correct. For example:
630 + 295 = 925 (addition)
925 – 295 = 630 (subtraction to check)
Answer
The answers are as follows:
 9 223
 682
 17 781
 596 487
 900 738
 217 889