You’ll need to “borrow” from the 3 in “32” (also known as regrouping), in order to turn that 2 into a 12. Cross off the 3 in “32” and make it a 2, while making the 2 a 12. Now, you have 12 - 7, which is equal to 5. Write a 5 below the two numbers you subtracted, so it lines up with the ones column in a new row.
In the problem 15 - 9, the first number, 15, is larger than the second, 9. In the problem 2 - 30, the second number, 30, is larger than the first, 2.
In the first problem, 15 - 9, your answer will be positive because the first number is larger than the second. In the second problem, 2 - 30, your answer will be negative because the second number is larger than the first.
For the problem 15 - 9, visualize a pile of 15 poker chips. Remove 9 of them and you’ll see that 6 of them remain. Therefore, 15 - 9 = 6. You can also think of a number line. Think of the numbers from 1 to 15 and then remove or go back 9 units to get 6. For the problem 2 - 30, the easiest thing to do is to reverse the numbers and then make the answer negative after you’ve subtracted them. So, 30 - 2 = 28, since 28 is just two less than 30. Now, make your answer negative since you determined at the beginning that it would be negative because the second number is larger than the first. Therefore, 2 - 30 = -28.
If you have a problem where both numbers don’t have the same amount of numbers after the decimal point, write a 0 in the empty spaces until they even out. For example, if you have the problem 5. 32 - 4. 2, you can rewrite it as 5. 32 - 4. 20. This won’t change the value of the second number while making it possible to subtract both numbers more easily.
Make sure to carry that decimal point down to the answer. It should read . 2 so far.
Note that the lowest common denominator of two numbers isn’t always one of the numbers. For example, the lowest common denominator of the numbers 3 and 2 is 6, because that’s the smallest number that is evenly divisible by both numbers.
Write the new problem like this: 13/10 - 6/10.
3x2 - 2x2 = x2 -5x - 2x = -7x 2y - y = y -z - 0 = -z
3x2 - 5x + 2y - z - (2x2 + 2x + y) = x2 - 7x + y - z
