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Reasoning about factors and multiples

CCSS.Math:

Video transcript

- [Instructor] We're told we know that five times three is equal to 15. Yep, that's true. So which of the following statements are also true? And it says to choose two answers. So pause this video and see if you can work through that. All right, now let's go through them one by one. So this first one says, "Three is a multiple of 15." Now, in order for three to be able to be a multiple of 15, that means that we can multiply 15 by some whole number to get to three. But a multiple of 15, we're thinking 15, 30, 45, it's not gonna be three. What whole number can I multiple 15 by to get three? If I multiply 15 by one, I'm already at 15. So this is not going to be our choice. And since it say pick two answers, well, we might be able to figure out it's these. But let's just read them to make sure that they make sense. 15 is a multiple of three. So that means I can multiply three times some whole number to get to 15, and we know what that whole number is. It's five. They tell us right over there. Five times three is 15. So 15 is a multiple of three. 15 would also be a multiple of five 'cause I can multiply five by the whole number three to get to 15. So I like this choice. Five is a factor of 15. Well, a factor, factors of a number are numbers that you can multiply together to get that number. So five is a factor of 15, and three is a factor of 15, because five times three is 15. So this one is also true. It would've also been true if they'd said three is a factor of 15, or if they'd said 15 is a multiple of five. Any of those would have been true statements based on what we know, that five times three is equal to 15.