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Current time:0:00Total duration:1:57

Addition and subtraction with number lines

Video transcript

which number line shows 47 plus 22 let's see this first number line we're starting at 47 then we add 20 to get to 67 and then we add 2 to get to 69 so if you add 20 and then you're adding to your adding 22 so this one seems right so let's see why these choices don't seem right so this one we add 2 to get to 49 and then 2 more to get to 51 well this isn't adding 22 this is adding 2 plus 2 this is adding 4 to add 22 you have to add 20 and then 2 and this choice right over here we are adding 20 and then we're adding 2 but we're not starting at 47 we're starting at 74 so this is this is 74 plus 22 so I definitely feel good about that choice right over there let's do a few more examples which number line shows 93 minus 76 so let's see in all of these choices we're starting at 93 here in this first choice we subtract 7 and then 6 but as subtracting 76 you want to subtract 70 and then you want to subtract 6 not just 7 so I don't like this first choice here we subtract 60 and then we subtract 7 but that's subtracting 67 not 76 we got to subtract 7 tens 7 tens and then 6 ones so here we're subtracting 7 tens we're subtracting 70 and then we are subtracting 6 ones so that's definitely that's definitely going to be the right choice so let's see maybe maybe one more just for just for fun which number line shows 12 plus 87 so all of these start off at 12 and we're going to want to add 80 and then add 7 8 tens and 7 ones and let's see this one adds 80 and then we add 7 so yep feel good about that one right over there