# Carrying and Borrowing

Carrying and borrowing in Modmath is done using two keys on the keypad: the corner box key and the strikethrough key. In this example we will use these keys to write and solve a subtraction problem, but these keys can also be used to write and solve other types of equations. The corner box key and the strikethrough key are located on the left side of the keypad if the keypad is not extended. If the keypad is in the extended position (like the example below) these keys are in the middle section.

* The corner box key has four location options: top left, top right, bottom left, and bottom right. Long tap (tap and hold) the key and choose the location you want to use.

Step 1 - Write your equation on the workbook using the keypad. The selected cell will automatically move from left to right after tapping a key on the keypad. In this equation we will be using the ones, tens, hundreds, and thousands "columns method" to solve our problem. Protip: You can change the default direction of the cursor to right to left in advanced settings.

Step 2 - We need to subtract 6 from 2 in the ones column. Given that 6 is greater than 2, we need to borrow from the tens column. Select (tap) the cell with the 3 in the tens column. Then tap the strikethrough key to add a slash through the 3. Next, tap the corner box key to add an empty box to the upper left corner. With the corner box selected (it will be selected once you add it or you can tap it to select it) tap the number 2 to add it to the corner box.

Step 3 - Now that you have borrowed from the tens column you can add it to the ones column. Select the cell with the 2 in it and tap the strikethrough key to add a slash. Next, with the cell with the 2 still selected, tap the corner box key to add a corner box to the upper left. Add the number 12 to the corner box. You can now subtract 6 from 12. Add the remainder (6) to the ones column under the horizontal line.

Next, we are going to repeat the process for the tens, hundreds, and thousands columns using the same process of selecting a number, adding a slash using the strikethrough key and borrowing using the corner box key.

In the next part of this equation we need to subtract 8 from 2 in the tens column. Given that 8 is larger than 2, we have to borrow from the hundreds column.

Step 4 - Select the 0 in the hundreds column and tap the strikethrough key to place a slash through the number. With the cell with the 0 still selected tap the corner box key to add a box to the upper left. With the corner box selected, type the number 9. Since we need to borrow from the thousands column to add to 0 in the hundreds column, select the 1 in the thousands box. Tap the strikethrough key to add a slash, then tap the corner box key to add a box to the upper left. With the corner box selected, type 0 to add this number. Lastly, select the corner box in the tens column and change the number from 2 to 12.

Step 5 - Now you are ready to solve the problem. In the tens column subtract 8 from 12 and add the number 4 under the horizontal line. In the hundreds column 9 minus 9 is 0, and since we borrowed from the thousands column already we are left with 0 in the thousands column.

Congratulations, you've arrived at the correct answer. 1032 - 986 = 46!