Distributive property algebraic expressions | Arithmetic properties | Pre-Algebra | Khan Academy


Let’s do some problems with
the distributive property. And the distributive property
just essentially reminds us that if we have, let’s say, a
times b plus c, and then we need to multiply a times this,
we have to multiply a times both of these numbers. So this is going to be equal to
a times b plus a times c. It will not be just a
times b then plus c. And that makes complete sense. Let me give you an example. If I had said 5 times 3 plus
7, now, if you were to work this out using order of
operations, you’d say, this is 5 times 10. So you’d say, this is 5 times
10, which is equal to 50. And we know that that’s
the right answer. Now, use the distributive
property, that tells us that this is going to be equal to 5
times 3, which is 15, plus 5 times 7, which is 35. And 15 plus 35 is
definitely 50. If you only multiplied the 5
times the 3, you’d have 15, and then plus the seven, you’d
get the wrong answer. You’re multiplying 5 times
these things, you have to multiply 5 times both
of these things. Because you’re multiplying
the sum of these guys. Anyway. Let’s just apply that to a
sampling of these problems. Let’s do A. So we have 1/2 times
x minus y minus 4. Well, we multiply 1/2
times both of these. So it’s going to be 1/2
x minus 1/2 y minus 4, and we’re done. Let’s do C. We have 6 plus x
minus 5 plus 7. Well, here there’s actually
no distributive property to even do. We can actually just remove
the parentheses. 6 plus this thing, that’s the
same thing as 6 plus x plus negative 5 plus 7. Or you could view this
as 6 plus– So this right here is 2, right? Negative 5 plus 7 is 2,
2 plus 6 is 8, so it becomes 8 plus x. All right. Not too bad. That was C. Let’s do E. We have 4 times m plus 7 minus
6 times 4 minus m. Let’s do the distributive
property. 4 times m is 4m plus
4 times 7 is 28. And then we could
do it two ways. Let’s do it this way first.
So we could have minus 6 times 4 is 24. 6 times negative
m is minus 6m. And notice, I could have just
said, times negative 6, and have a plus here, but I’m
doing it in two steps. I’m doing the 6 first, and then
I’ll do the negative 1. And so this is going to be
4m plus 28, and then you distribute the negative sign. You can view this as a negative
1 times all of this. So negative 1 times
24 is minus 24. Negative 1 times minus
6m is plus 6m. Now you add the m terms.
4m plus 6m is 10m. And then add the constant terms.
28 minus 24, that is equal to plus 4. Let’s go down here. Use the distributive property
to simplify the following fractions. So I’ll do every other
one again. So the first one is, a
is 8x plus 12 over 4. So the reason why they’re
saying the distributive property, you’re essentially
saying, let’s divide this whole thing by 4. And to divide the whole thing by
4, you have to divide each of the things by 4. You could even view this as,
this is the same thing as multiplying 1/4 times
8x plus 12. These two things
are equivalent. Here you’re dividing each
by 4, here you’re multiplying each by 4. If you did it this way, this is
the same thing as 8x over 4 plus 12 over 4. You’re kind of doing a adding
fractions problem in reverse. And then this 8 divided
by 4 is going to be, this’ll be 2x plus 3. That’s one way to do it. Or you could do it this way. 1/4 times 8x is 2x, plus
1/4 times 12 is 3. Either way, we got
the same answer. C. We have 11x plus 12 over 2. Just like here. We could say, this is the same
thing as 11– We could write it as 11 over 2x, if we like. Or 11x over 2, either way. Plus 12 over 2 plus 6. And let’s just do one more. E. This looks interesting. We have a negative out in front,
and then we have a 6z minus 2 over 3. So one way we can view this,
this is the same thing, this is equal to, negative 1/3
times 6z minus 2. These two things
are equivalent. Right? This is a negative 1/3. You could imagine a
1 right out here. Right? Negative 1/3 times 6z minus 2. And then you just do the
distributive property. Negative 1/3 times 6z is
going to be minus 2z. And then negative 1/3 times
negative 2, negatives cancel out, you get plus 2/3. And you are done.

34 Replies to “Distributive property algebraic expressions | Arithmetic properties | Pre-Algebra | Khan Academy

  1. Sal, I don't know if you'll read this but this is where my voyage begins in mathematical exploration. I have taken algebra and statistics at my local community college and have decided that I would like to minor in mathematics. I started to teach myself calculous but found my math to be a little rusty so here I am. Let's see if I'll be a math wiz in 2 years like I'm hoping. Hey, it took Newton less time to invent calculous than most freshman take to learn it in college.

  2. 6 divided by 3 becomes 2, now 1 over 3 is divided into 3 and becomes a unicorn, now take 12 and make that a bear and then remember it needs a orange in its butt so that becomes another 12…

  3. I'm doing an extra credit project in which I have to ask a question so my question is why were the parenthesis brought down on the 4(m+7)-6(4-m) example after being distributed already?

  4. Given 1/2(5), is the answer one tenth: 1/(2(5)) or half of 5: (1/2)(5)?
    Does the distributive property count as a parentheses operation, overriding the left to right rule of multiplicative order of operations?

  5. I promise you one day you will get a big donation from me. This coming from someone who HATED school and now can spend hours without break learning. I want to thank you and your team for making Khan Academy!

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