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### Course: Pre-algebra > Unit 1

Lesson 1: Factors and multiples# Reasoning about factors and multiples

Use the equation 3x5=15 to understand the relationship between factors and multiples. Created by Sal Khan.

## Want to join the conversation?

- um... whats a factor of 78 plz help im cofuzed🤔(23 votes)
- The factors of 78 are 1,2,3,6,13,26,39,78.

To figure these out be sure to check the previous lesson on divisibility checks.(15 votes)

- how do i do fector pair?(8 votes)
- You don't exactly do factor pairs. The factor pairs of a number are various pairs of numbers that when multiplied will get you to that number. So, say with prime numbers, there's only one factor pair: 1 and itself. For composite numbers, the factors are more than two. So, answering your question, the factor pairs of a number will always be easy to figure out once you know what type of number it is. To organize a factor pair, just type\write say for 67, 1 and 67 or 1x67.(2 votes)

- what are factors of 82?(4 votes)
- 82 is a composite number and has 4 factors which are 1, 2, 41 and 82!
**Happy Learning**!(5 votes)

- wait if a multiple of 20 is 5 and 4 than a factor of 20 would be 5 and 4 how the heck am i supposed to know what is wich(4 votes)
- Multiples of 20 are 20, 40, 60, etc.

Factors of 20 are 1, 2, 4, 5, 10, 20(1 vote)

- so i just can use multiples?(4 votes)
- What is a factor of 76 I’m really confused(3 votes)
- The factors of 76 are 1, 2, 4, 19, 38, and 76.(2 votes)

- what is a factor of 138 pls help

me(2 votes)- 1, 2, 3, 6, 23, 46, 69 and 138(3 votes)

- 15n's a good answer(2 votes)
- its feel to much work(2 votes)

## 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.