Multiplying decimals example | Decimals | Pre-Algebra | Khan Academy
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Multiplying decimals example | Decimals | Pre-Algebra | Khan Academy

We’re asked to multiply 32.12,
or 32 and 12 hundredths, times 0.5, or just 5 tenths. Now when you multiply decimals,
you multiply them the exact same way you would
multiply whole numbers, and then you count the number of
spaces behind the decimal you have in your two numbers you’re
multiplying, and you’re going to have that many spaces
in your product. Let me show you what
I’m talking about. So let’s just multiply
these two characters. So we have 32.12 times 0.5. And when you write them out, you
can just push both of them all the way to the right. You could almost ignore
the decimal. Right now, you should write the
decimal where they belong, but you can almost pretend that
this is 3,212 times 5, and then we’ll worry about
the decimals in a second. So let’s get started. So if we were just multiplying
5 times 3,212, we would say, well, 5 times 2 is 10. Regroup the 1. 5 times 1 is 5, plus 1 is 6. 5 times 2 is 10. Regroup the 1. And then finally, you have 5
times 3 is 15, plus 1 is 16. And then we don’t have
any other places. If we were just doing this as
05, we wouldn’t multiply 0 times this whole thing. We would just get 0 anyway. So just 5 times 3,212 gives
us this number. But now we want to care
about the decimals. We just have to count the total
number of spaces or places we have behind the
decimal point in the two numbers we’re multiplying. So we have one, two, three
spaces, or three numbers, to the right of the decimals in
the two numbers that we’re multiplying. So we need that many numbers to
the right of the decimal in our answer. So we go one, two, three, put
the decimal right over there. So 32.12 times 0.5 is 16.060. And this trailing zero right
here we can ignore, because it’s really not adding any
information there. So we could just write
this as 16.06. The last thing you want to do
is just make sure that this makes sense. You have a number that’s
almost 32, and we’re multiplying it by 0.5. Remember, 0.5 is the same thing
as 5 over 10, which is the same thing as 1/2. So we’re really multiplying
32.12 times 1/2. We’re trying to figure out what
one half of 32.12 is. And half of 32 is 16, and half
of 0.12 0.06, so this makes complete sense.

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100 thoughts on “Multiplying decimals example | Decimals | Pre-Algebra | Khan Academy

  1. this i hope will help me, cause last year when i was in 5th grade, i was absent the day we were learning about this and no one ever told me how, and in 6th grade (2/2/2017) we were doing multiplying decimals bingo. since i had no absolute knowledge of this, im praying this will help. so im putting it on loop and listening to it for an hour.

  2. This is simply didactic instruction and has no element of learning. People who tack in are actually self selecting……they actively WANT to know. This is boring teaching as it has always been done.

  3. so i have this problem, i am trying to find out this lmao, but a different version, i have 7.9 x 3, for example i do need some help.. haha

  4. Me Before: OMG THIS IS SO HARD! UGH!
    Me Watching: Hmmm…Ima try my problem again, maybe this time I'll get it..

    I always use the calculator, but my teacher always tells us to SHOW our work, and I usually did that. This time I used the calculator first and then I couldn't get it. xd Thank you so much Khan Academy!

  5. Thank you, you saved my life. I'm probably gonna pass the 6th grade now. All I need is one F to fail, so I really gotta try this year.

  6. thank you so much for this. i’m in 6th grade and decimals are so hard. my teacher is the worst teacher ever but this is very helpful

  7. Bruh I watched this video because half the time I and my 5th grade class ask my teacher DO YOU EVEN ENGLISH WOMAN???

  8. Thank you Khan Academy!! 😭😭😭 I’m 23 years old and have NEVER been strong at math, and all my teachers growing up in school here in California never wanted to take the time and REALLY TEACH ME, One on One so I grew up with a HUGE insecurity and fear of math. But that’s negatively affected my job hunt and now I’m on the prowl to re-learn what I didn’t understand growing up, and you guys are FANTASTIC!!! Thank you again! Keep up the amazing work 😊😘🤩👏🏾

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