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Math 5: Adding Fractions 119 Views
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Description:
If you've ever baked anything, chances are you've worked with a few fractions. For the sake of your loved ones, though, we hope you've never baked anything like this...
Transcript
- 00:14
Doug’s Grandma isn’t like the other Grandma’s on the block. [Doug's Grandma riding a motorcycle down the street]
- 00:17
For starters, she drives a motorcycle and raises alpacas…
- 00:19
Pretty strange…but the strangest thing to Doug?
- 00:22
Definitely Gram's taste in food. [Doug looking sad in his Grandma's kitchen]
- 00:23
Today she’s making something called Squid Bits…
Full Transcript
- 00:25
Which are kinda like what would happen if a squid married a granola bar and they had
- 00:29
babies. [Squid-topped granola bars on a plate]
- 00:30
Yep, life with Grandma is never dull.
- 00:33
Grandma only has one very small pan, so she needs to make sure ahead of time that the
- 00:36
amount of ingredients in the recipe will fit.
- 00:38
So she starts by adding up all the ingredients. [Grandma making a list of all the food ingredients]
- 00:41
She needs 3/4 of a cup of old-fashioned oatmeal and 1/4 of a cup of wheat germ.
- 00:45
These are easy to add because 3/4 and 1/4 have the same denominator…AKA the number
- 00:50
at the bottom of the fraction is the same…in this case 4.
- 00:53
When fractions have common dominators, all we have to do is add the numerators…AKA [Adding numerators and denominators on a notepad]
- 00:57
the numbers on the top of the fraction...in this case 3 and 1.
- 01:00
So Grandma adds 3/4 to 1/4 to get 4/4.
- 01:04
Doug is impressed that his Grandma knows how to do this…
- 01:07
Though he’s less impressed by the fact that she lets her alpaca in the kitchen while she [Alpaca stood in the kitchen with Grandma and Doug]
- 01:10
cooks.
- 01:11
The health inspector would probably give her a grade D.
- 01:13
It’s not long before Grandma runs into trouble.
- 01:16
Her recipe calls for 2/3 of a cup of freshly chopped squid.
- 01:19
And she has no idea how to add 2/3 to the 4/4 she’s already got.
- 01:24
She has unlike denominators now.
- 01:25
What’s a kooky Grandma to do? [Grandma looking confused at the fraction of chopped squid]
- 01:28
Doug feels bad and says he’ll help her…
- 01:30
As long as she promises to not make him eat the squid bits when they’re done. [Doug offering help to his Grandma as Alpaca walks by]
- 01:33
Grandma swears on the soul of her alpaca that Doug will be spared.
- 01:37
So Doug tells her "the main thing to remember is that we can’t add fractions unless they’re
- 01:40
denominators are the same."
- 01:41
To add fractions with unlike denominators, she has to find what’s called the least
- 01:45
common denominator.
- 01:46
Sometimes it helps to think of it as the least common multiple, too.
- 01:50
So with 3 and 4 the LCD is 12 because it’s the smallest common multiple of 3 and 4. [4 multiplied by 3 = 2 highlighted on a notepad]
- 01:54
Doug’s Grandma still isn’t quite getting it.
- 01:56
Okay…yeah…both denominators should be 12, but how are they supposed give both fractions
- 02:01
that kind of makeover? [A fraction receiving a makeover]
- 02:02
Doug tells her it’s no big deal.
- 02:04
They just have to multiply both the numerator and the denominator by the number that will
- 02:07
make the denominator 12.
- 02:09
So with 2/3 they multiply it by 4/4 to get 8/12… [Fractions multiplied together wrote in a notepad sheet]
- 02:13
And with 4/4 they multiply by 3/3 to get 12/12.
- 02:18
Grandma gets excited because she’s back in familiar territory. [Grandma looking excited in the kitchen]
- 02:20
Now that the fractions have a common denominator, all she has to do is add the numerators.
- 02:24
So that’s…8/12 + 12/12 = 20/12
- 02:28
Doug tells her 20/12 is kind of a wonky fraction.
- 02:32
Grandma is slightly offended, but Doug tells her to relax…it’s easy to de-wonkify. [Doug telling Grandma to relax as Alpaca walks behind them]
- 02:36
The best thing to do is reduce the fraction.
- 02:38
To do this, he asks himself…What’s the biggest number that will go into both 20 and
- 02:43
12?
- 02:44
Bingo…he thinks…4.
- 02:45
So he divides 20/12 by 4/4 to get 5/3. [20 divided by 12 calculation written on a notepad]
- 02:49
Now, Grandma has the hang of it, and no other fractions with unlike dominators give her
- 02:53
any trouble.
- 02:54
It’s not long before her squid bits come out of the oven piping hot. [Squid bits on an oven tray]
- 02:57
She scoops one up and tells Doug to open wide.
- 03:00
Doug complains that she swore on the soul of her alpaca…
- 03:02
Sure…she says…but I had my fingers crossed behind my back. [Grandma's fingers crossed behind her back]
- 03:06
Poor Doug.
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