Positive number minus negatives.

When there is a negative sign in front of a number it means the "opposite" of that number.

So for instance -5 or negative five is the "opposite" of 5 which is -5.

So if you have a number like -3 what would it it's "opposite"? That would be 3.

so if you have two negatives its like taking the opposite of an opposite. so the opposite of -7 is 7.

Which is why in this case you would get 17 + 7 = 24.

Khan academy has a few videos on this which goes into much better explanation also has tons of information that should be able to help you with some mathematics.

https://www.khanacademy.org/math/cc-sixth-grade-math/cc-6th-negative-number-topic/cc-6th-number-opposites/v/opposite-of-a-number

I'm assuming you mean 17- (-7) = 24. It equals this because you are taking away negative, which means more positive. For example: Say you have $24, and you owe 7 dolars to a friend. If you didn't pay the 7 dollars, it would be negative $7 on your account because eventually you would have to pay it. That would be $17. But if you did your friend a favor, and he chose to take away your debt, you would have minused -7 dollars from your account, causing you to have 24 dollars!

By the way, if this helped at all, could you give me a 5 -star rating or 2?

Yes, it's called a double negative. Anywhere you see - - before a number, like 5 - -7, or  5 - (-7), then you flip both signs. This does not apply for positive numbers because you would never need two pluses. But, if you have a problem like 7 + -8, you simply flip both signs, and then get rid of the positive in front of the 8, because everyone knows that if a number has no negative sign, than it's positive