Math

Sarah Rebekah 13 · 2010-06-05 07:59:59

100x25?

bobbym · 2010-06-05 08:38:46

Hi Sarah;

1 0 0
x 2 5
--------
5 0 0 5 x 100
2 0 0 0 20 x 100
------------
2 5 0 0 Just added the columns

Sarah Rebekah 13 · 2010-06-07 04:33:14

Thanks.

bobbym · 2010-06-07 04:47:34

Hi Sarah;

Try this one for me.

15 * 100 See if you can get it. If not I will show you how.

Sarah Rebekah 13 · 2010-06-07 05:30:59

1500

bobbym · 2010-06-07 08:41:22

That's correct, very good.

Sarah Rebekah 13 · 2010-06-08 04:14:11

Thanks

John E. Franklin · 2010-06-11 07:52:03

Sarah, I will now do 23 x 45.

45
x 23
-------

3 times 5 is 15 so write down the 15
45
x 23
-------
15

3 times 4 is 12 so write down the twelve. Usually you carry but this way is new, no carrying needed.
45
x 23
-------
15
12

Now we go to the 2 in 23.
2 times 5 is 10 so write it down left a little because the 2 is left of the 3 in 23.
45
x 23
-------
15
12
10

Now do the 2 times the 4 and that's 8, put it left of the right side of the 10, so the
one's places don't line up, they are off by one.

45
x 23
-------
15
12
10
8
-------

Next, add up the four numbers:

15
12
10
8
______
5 is all alone, see nothing below it if you look exactly straight below the 5.
So 5 is the right digit in the 1's place.

15
12
10
8
--------
5

15
12
10
8
Next the 1 + 2 + 0 are in one column looking in the middle of the numbers.
1 + 2 + 0 is 3 so now you have
35 so far and you still need to have one more digit in the hundreds place on the
left of the 35.

15
12
10
8
-----------
Now add the 1+1+8 on the left of the numbers.
That is ten, now the answer is 1035.
So 23 times 45 should be 1035.

misheeru · 2010-06-11 11:40:55

Wow, John E., you really broke it down! Where were you when I was doing multiplication??

John E. Franklin · 2010-06-11 13:19:31

I guess I took a year off vacation by mistake...

misheeru · 2010-06-11 13:37:17

no no, it was a joke. I started multiplication when I was like 7. That was almost 10 years ago! I meant it as, where were you when I was struggling with it. Get it? Sorry, bad joke.

John E. Franklin · 2010-06-11 13:59:54

Yup, get it now. Thanks.
Now for a math problem.
Given that -40 Farenheit and
-40 Celcius are the same
temperature, come up with a
new formula to convert
between the two that uses this
information as closely as
possible. Also note that a
Farenheit degree times 9 is
equal to the size of 5 Celcius
degrees because Celcius
degrees are bigger.

Sarah Rebekah 13 · 2010-06-12 08:07:47

Good Job John.

John E. Franklin · 2010-06-14 05:01:02

Thanks Sarah, you can either carry at the end or while you do your multiplication.
There are different ways that all work.

John E. Franklin · 2010-06-14 08:45:33

Sarah, now I will do 9 x 13.
Then after that I will do 13 x 9, like
with the other number on the top.
Should get same answer.

13
x9
----

first do 9 times 3, that's 27.

13
x9
----
27

Next when you go to the 9 times 1
you have to remember that the
right side of the number will be
moved over a little to the left
one space. It won't be exactly
below the 27. This is because
The 1 is left of the 3 in 13, and
the 9 remains the same in
both cases.

13
x9
----
27

Now 9 times 1 is 9 so write that down, but a little to the left,
below the 2 of 27, not below the 7 of 27.

13
x9
----
27
9

Next add the 27 and the 9 up for the answer.

13
x9
----
27
9
-------

7 and nothing below it is 7 so
write down a 7. Some people
put a zero below the 7. You
can if you want to.

13
x9
----
27
9
-------
7

Next add the 2 and the 9 to make 11.
The right side of the 11 goes below the
2 and the 9.

13
x9
----
27
9
------
117

So that's your answer, it's 117.

John E. Franklin · 2010-06-14 08:56:04

Now I'll do

9
x 13
--------

This time you do 3 x 9 first.

9
x 1 3
--------
2 7

Now next since the 1 is to the left in 13, then the
next answer will be to the left 1 spot.
So do the 1 times the 9.

9
x 1 3
--------
2 7
9

See how the 9 ended up below the 2 ?

The 9 went below the 2 because the
right side of the 9, which is just the
9 since it only has one digit, which is
9. This 9 has to go left one from the
right side of the number above it.
The reason is because the 2 numbers
we multiply together to get that
number, one of them is left a
spot from the other 2 numbers
that are multiplied. This is
complicated to explain.

C
x A B
--------
BxC
AxC

So we are doing b times C
and then doing A times C.

The C's are the same, so
it is just the B and the
A that are different, so whichever
one is left of the other one,
put the rightside of the answer
to the left of the other ones
rightside of the number.
The right side of the number is
called the "one's place".

So basically you are lining up
the ten's place with the one's place
before you add them up.

Bye!

Sarah Rebekah 13 · 2010-06-15 05:54:39

You are Welcome nice Job agin.

Math Is Fun Forum

#1 2010-06-05 07:59:59

Math

#2 2010-06-05 08:38:46

Re: Math

#3 2010-06-07 04:33:14

Re: Math

#4 2010-06-07 04:47:34

Re: Math

#5 2010-06-07 05:30:59

Re: Math

#6 2010-06-07 08:41:22

Re: Math

#7 2010-06-08 04:14:11

Re: Math

#8 2010-06-11 07:52:03

Re: Math

#9 2010-06-11 11:40:55

Re: Math

#10 2010-06-11 13:19:31

Re: Math

#11 2010-06-11 13:37:17

Re: Math

#12 2010-06-11 13:59:54

Re: Math

#13 2010-06-12 08:07:47

Re: Math

#14 2010-06-14 05:01:02

Re: Math

#15 2010-06-14 08:45:33

Re: Math

#16 2010-06-14 08:56:04

Re: Math

#17 2010-06-15 05:54:39

Re: Math

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