Intro to adding negative numbers
- We have three different number lines here, and on each number line they mark off a couple of these marks, this is negative two this is negative 10, negative five, negative 11, and then we need to figure out what the blue dot represents. And as a little bit of a hint, each mark here is not necessarily incrementing by one, it could be by more than one. So I encourage you to pause this video, and to try it on your own. Try to figure out what number does this blue dot represent on these different number lines? So let's tackle this first one. So we're gonna go where they gave us this mark is negative two, this is negative 10, and we need to figure out this blue one that's further to the left of negative 10. Well just going from negative two to negative 10, what has to happen to negative two to get to negative 10? Well we'll have to subtract eight. And so if we move two to the left, that's the equivalent of subtracting eight. So if we move two to the left again, that's subtracting eight again. So this must be negative 18 and so if we move two to the left again, that also must be subtracting eight. Negative 18 minus eight, would get us to negative, that gets us to negative 26. Now another way we could have thought about it is, if we jump two to the left and that's negative eight, then one jump to the left is gonna be negative four. So you could say "Well this is negative four", that would get you to negative six, then negative four again gets you to negative 10, then this would be negative 14, negative 18, negative 22, negative 26. Now let's tackle this one. So here we're gonna, we have to figure out what this blue dot here is on the right. So if we started at 11, you make two jumps to go to negative five. So what do I have to add to negative 11 to get to negative five? Well I have to add six. So if I add six over two jumps, that means that each of these jumps, that must be plus three, and this one must be plus three. So now each mark we just add three. So negative five plus three... So plus three is gonna get us to negative two. Plus three gets us to positive one, negative two plus three is positive one, plus three gets us to four. So here we got to negative 26, here we get to four. Now let's tackle this one. So we're at negative seven, or this is negative seven this is one and then we have to figure out this mark right over here. So if you take two jumps to the right, from negative seven to one, how much did we have to add? Well to get from negative seven to one, you have to add eight. You have to add eight. So then if we make another two jumps to the mystery number that means we added eight again. So one plus eight is nine. Another way we could have thought about it, if we added eight over two jumps that means we added four on each jump. So this one must be negative three, add four you get to one, add four you get to five, add four you get to nine.