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Current time:0:00Total duration:3:32

CCSS Math: 3.OA.D.8

Abe went running 4
days this past week. He ran 9 kilometers on each day. In that same week, Beth ran
15 fewer kilometers than Abe. How many kilometers
did Beth run that week? So I encourage you
to pause this video and to try this on your
own, try to figure out, how many kilometers
did Beth run that week? So there's a couple
of ways to think about it or a couple of
ways to visualize it. The first thing we
might want to do-- in fact, the first thing
we definitely want to do-- is to figure out, well, how
far did Abe run in that week? Well, he went 4 days, and each
day, he went 9 kilometers. So we could say
that he went-- let me do that blue color-- 4 days
times 9 kilometers per day. And we could visualize that. So this is how much
he went in one day. This is how much he
went in two days. This is how much he'd
go in three days. This is how much he
would go in four days. So what is this? What is 4 times 9 kilometers? Well, this is essentially
9 plus 9 plus 9 plus 9. So we could just add up the 9's. 9 plus 9 is 18, plus
9 is 27, plus 9 is 36. So he ran a total
of 36 kilometers. Now, that's not what
they're asking us for. They're asking us for
the number of kilometers Beth ran that week. And they tell us that she ran
15 fewer kilometers than Abe. So this right over here,
Abe's total distance-- if we start from
here, and we were to go all the way over the
week, all the way to here, he ran 36 total kilometers. Beth ran 15 fewer
kilometers than Abe. So let's go back 15 kilometers. So Beth ran 15 fewer
kilometers than Abe. So that's 15 fewer kilometers. And so the number of
kilometers that Beth ran would be this distance. It would be this
distance right over here. So this is kilometers Beth ran. Let me write it like this--
Beth's distance in the week. Beth's distance would be this
distance right over here. So how do we figure that out? Well, if we say Beth's
distance-- let's just use the letter
B for shorthand. So Beth's distance
plus 15 kilometers is going to be equal
to Abe's distance, is going to be equal
to 36 kilometers. Or another way of thinking
about it-- Beth's distance is going to be equal to Abe's
distance, so 36 kilometers, minus 15. So what is Beth's distance
going to be equal to? Well, 36 minus 15--
6 minus 5 is 1. 30 minus 10 is 20. So it's going to be 21. So Beth's distance
is 21 kilometers.