Working with negative numbers can be confusing for students. Often times, students understand that when they see a question in which you subtract 7, they should get more negative. However, when they come across a question like -9 - 7, their immediate response is -2.
In my experience, it helps students to use a number line to visualize their starting point and where they are going. Pairing a number line, with guiding questions can help students to begin breaking down and feeling more comfortable working with negative numbers.
The student can count to the left 7 times and arrive at the answer -16. From here, it is useful to point out that when you begin with a negative number and subtract some value, you have really added the two numbers together.
This brings me to a tip my math teacher gave me when we began learning negative numbers. Subtracting a positive number, it is the same as adding a negative number. In other words, you can also think of -9 - 7 as -9 + -7. When looking at the problem like this, it is really easy to see that to solve this question, you need to add the values 7 and 9. Since you begin with a negative number and become more negative, the answer is negative.
The other type of question involving negative numbers that students can find confusing is subtracting a negative number.
In this case, subtracting a negative number is the same as adding a positive. This question can also be written as -15 + 7. In this form, it is easier to see that to solve the question, it is necessary to become more positive (add 7).
There are many ways to think about and solve any math problem. The most important thing is to help your child visualize the problem so it makes sense for them. Then they will be able to solve it and more difficult questions in the future.