To add or subtract large numbers, stack the numbers on top of each other so that all similar digits (ones, tens, hundreds, and so forth) form columns. Then work from right to left. Do the calculations vertically, starting with the ones column, then going to the tens column, and so forth:

• When you’re adding and a column adds up to 10 or more, write down the ones digit of the result and carry the tens digit over to the column on the immediate left.

• When you’re subtracting and the top digit in a column is less than the bottom digit, borrow from the column on the immediate left.

## Sample questions

1. Add 35 + 26 + 142.

203. Stack the numbers by aligning the ones place. Add the columns from right to left:

Notice that when you add the ones column (5 + 6 + 2 = 13), you write the 3 below this column and carry the 1 over to the tens column. Then, when you add the tens column (1 + 3 + 2 + 4 = 10), you write the 0 below this column and carry the 1 over to the hundreds column.

2. Subtract 843 – 91.

752. Stack the numbers by aligning the ones place. Subtract the columns from right to left:

When you try to subtract the tens column, 4 is less than 9, so you borrow 1 from the hundreds column, changing the 8 to 7. Then place this 1 in front of the 4, changing it to 14. Now you can subtract 14 – 9 = 5.

## Practice questions

1. Add 129 + 88 + 35.

2. Find the following sum: 1,734 + 620 + 803 + 32 = ?

3. Subtract 419 – 57.

4. Subtract 41,024 – 1,786.

The following are the answers to the practice questions:

1. 252

2. 3,189

3. 362

4. 39,238