Welcome to Excel and Business Math video number 15.
Hey.
In this video we've got to talk about multiplying fractions,
dividing fractions, and even a little bit about dividing
and units.
Now we're going to see how to do all of these by hand and then
a little bit in Excel.
All right.
Now we're going to go over to PowerPoint
to see how to do these calculations by hand.
All right.
First we want to look at how to multiply fractions.
It's pretty straightforward.
You multiply the numerators, the denominators,
and if it needs to be reduced, you reduce it.
Our examples are going to be hey,
we're going to take 6 divided by 8 and multiply by 2 times 12.
We'll say equals, draw a long bar,
and I simply multiply the numerator.
6 times 2.
And then multiply the denominators.
8 times 12.
And I could just do straight multiplication.
That would be 12 and 96.
But I'm going to do some canceling here.
I see there's a six there, so I'm going to leave a one.
Guess what?
There's a 6 in there.
How many?
2.
Now I see a 2 in the denominator and the numerator.
So look at that.
I'm left with 1 over 8.
So multiplying fractions is straightforward.
Just multiply the numerators, multiply the denominators,
and reduce.
Now let's go to the next slide.
Dividing fractions.
Simply has one extra step.
At the beginning we invert or flip the second fraction
in the denominator.
Then we multiply.
Then we reduce.
So if I'm taking 6 divided by 12 and I'm going to
divide that by 1/2.
Well guess what?
I get to flip the second fraction, the denominator.
So 6 divided by 12, that stays exactly the same.
Now we multiply and I invert.
And then I get 6 times 2 over 12 times 1.
Oh, before I do that, why don't we do this?
How many 6's are in 6?
There's 1.
How many 6's are in 12?
Oh, look at that.
2.
So we're left with some number over that same some number.
Which of course, any time the numerator and denominator
are the same, that's that magic number 1.
Now I want to go to the next slide and talk about units.
Sue and Abby drove nonstop for 3,000 miles
and drove 60 miles per hour the whole trip.
How long did it take them to drive 3,000 miles?
Now, we're not going to do this as a word problem
and set everything up, but we are going
to write down our variables.
Number of miles was 3,000.
Speed equals 60 miles.
Notice both numbers have miles as units,
but this one has per hour.
Remember that per, that means division.
Now in order to find out how fast they were driving,
I need to take 3,000 miles and divide by the number
of miles per hour.
But watch what happens when we do this.
And we're going to keep the unit.
So miles divided by--
I'm going to ride 60 miles and I'm
going to do a division bar because remember
per hour, that's one hour.
What really happens when I do this
is I could rewrite this 3,000 miles divided by 60 miles per 1
hour.
Notice this is division, so we can invert the second fraction
or the denominator.
So down here I'm going to say hey, 3,000 miles.
And I could have a 1 here.
Any number over 1 is itself, but now I'm
going to use multiplication and I have to flip this.
So 1 hour over 60 miles.
I'm running out of space here.
I'm going to say equal and I'm going to rewrite this 3,000.
I'm going to use an M. Times 1 hour over--
and I'm going to leave that one and just put 60 miles.
Now we want to reduce the numbers,
so we're going to have to break apart the 60 and the 3,000
in just some factors we can cancel.
But we also want to learn that we can cancel units.
Now hey, let's do this trick.
There's a zero.
That means we're canceling at 10 in the numerator
and the denominator, but we're totally
allowed to cancel units.
If they're in the numerator and denominator, they cancel.
So we're left with 300 hours divided by 60
Notice how that's convenient.
The miles canceled out.
The real answer to our question really is in hours.
Remember, how long did it take them to drive 3,000 miles?
But we still have a little bit of work to do.
So I'm going to say equals.
How many 6's are in 300?
Well I don't know for sure, but I do know 6 times 5
is 30, right?
So 6 times 50.
No.
We weren't supposed to have that.
Divided by 6 and I have the hours up here.
Now we can cancel the 6 and there's our answer.
So it took them 50 hours.
And I guess I better put it an S there.
So here we saw an example of dividing fractions, inverting
and multiplying, so we saw multiplying again.
And then we saw that we're allowed
to cancel not only factors like our 6, 6, but also units.
All right.
Now we want to go over to Excel and take
a look at multiplying and dividing fractions in Excel.
Now over here in Excel, we're on the sheet multiply and divide.
Multiplying, pretty straightforward.
We have 1/2 times 1/4.
I simply make a formula and multiply the first one times
the second one.
Now when I enter this, the cell references of course
are going to pull the number formatting.
So when I control enter it shows me that as a fraction.
That's number formatting.
When you're multiplying the operation is easy.
Just make sure that you're displaying it
with the correct reduced fraction.
Now dividing 6/12 divided by 1/2.
Well if we apply our rule, then we
flip the second one, the denominator,
and simply multiply.
6 times 2 is 12, and 12 times 1 is 12.
So if we were to multiply these times the inverted or flipped
one, we would get 12 over 12.
If we did the formula again times this one,
now it's going to pull through the cell references
the number formatting.
But I can come right up to number group and apply general.
And sure enough, any number divided by itself is 1.
In Excel, though, we don't have to flip the second fraction
and then multiply.
We can simply do our division.
There's the first one divided by the second one.
And as long as we make sure that the number is
displayed as a reduced fraction, we're good to go.
All right.
That's just a little bit about multiplying and dividing
fractions here in Excel and over by hand.
We also talked about canceling units, not just factors
when they're both in the numerator and denominator.
All right.
If you like that video, be sure to click that thumbs up,
leave a comment, and sub.
There's always lots more videos to come from Excel
is Fun, including next video number 16.
We'll talk about adding and subtracting fractions.
All right.
We'll see you next video.